diving into politics for the first time

Well right now that is changing dramatically. The "alt-right" is drastically changing what it means to be a Republican. Meanwhile Bernie supporters and an organization called the "Justice Democrats" are drastically redefining what it means to be Democrat.
This is actually one of the primary reasons Trump won. Everyone in the USA is sick of the status quo, e.g. "the way things are". Gallup polls are showing faith in public institutions are at all-time lows.
No one thought Trump had a chance, all through the primaries. More relevantly, no Republicans thought Trump had a chance.
Bernie supporters knew Bernie was the obvious best choice to defeat a Republican candidate. Hillary squashed the Democrats' chance of winning this past election.
Because Trump represents the new Right Wing in politics in the USA. Bernie represents the new Left Wing.

This is the era of Millennials coming of age. Baby Boomers are dying off in droves.
The details of your question - what is a Democrat and what is a Republican in this day and age - are being hashed out in the Courts and in Congress and we speak.

If I may add a bit more commentary, I would advise you to check out the history of the right-left spectrum and also the political compass.

The ideas of "right wing" and "left wing" came about during the French Revolution. Shortly after our own Revolutionary War, the French cast off their Monarchy as well, and went with a Parliament.
To the right of the speaker sat the Aristocracy and the Clergy, to the left sat the commoners.
Originally being "right-wing" meant you thought we should still have a king and that rich people and royals should be in power and that as a Christian Nation the Church should still have power over issues like abortion and what is taught in school.
Originally being "left-wing" meant that you thought the people should have the power to make decisions for themselves and that the King and the Pope and all other existing forms of authority should fck right the fck off like a good old revolutionary....

A big part of why this flipped is Big Business.
Capitalism was new in the late 1700s. Before then, the Crown and the Church did control all the wealth. In these new capitalist societies, the market controlled the wealth and we saw these things such as "Rags to Riches" and The American Dream.
Corporations, in the early days, were the best of most effective way for The People to stake their power claims against the old institutions such as the Monarch or the Church.
Trouble is, the corporations became the new Power Elite. I think we can all agree that there is a huge difference between megacorps like McDonalds, Pfizer, Exxon-Mobil, etc and small mom'n'pops run by That Guy You Know who is still in debt and struggling to pay off his business loan.
These issues need to be legislated!

Fast forward to the present and now we have megacorps like the ones listed above, boasting revenues larger than the GNPs of countries and becoming major power players in and of themselves.
"Mike From Down The Street" is never going to experience what Jeff Bezos or Bill Gates or Warren Buffet is experiencing. They live in completely different universes.

Corporations, originally designed to protect the people from the Power Elite, have now become the Power Elite.
This was going on way back around the advent of Communism, when Standard Oil and American Tobacco.
Some leftists went even further left, all the way to Communism. Others stopped at Socialism or Social Democracy. Labor Unions were created to protect workers' rights (e.g. protect The People from the Corporations). The 40-hour work week was passed, overtime was created, child labor laws were passed, workman's comp, affirmative action, paid vacation health insurance and other benefits, job securities, contracts, retirement, 401ks, social security....
Other leftists took a middle-of-the-road USA Democrats approach, which really has just been shifting further and further right and more authoritarian until we see it degrade into that disgusting mess of a campaign Clinton put on.
And then there's Bernie: actively fighting to get even more rights and benefits for the people, and to get money out of politics and stifle corruption.
See all that neat stuff I mentioned a couple paragraphs ago about leftists in the US getting workers rights and safety regulations, well, that's been corrupted too. :/ Labor Unions have mostly been bought out. Union bosses take bribes from corporate leaders and don't actually do anything to protect The People anymore.

This is where the political spectrum doesn't make sense anymore. Some leftists have flip-flopped back to the right hoping "the enemy of my enemy will be my friend". Other leftists have pushed even further left.
The political compass, on the other hand, attempts to plot 2 different axes, realizing that social and fiscal politics are completely different.
So you have the Democrats, who are socially liberal. As far as society, do whatever you want. Be an atheist, be gay, smoke weed, use a different bathroom.. whatever, who cares, freedom! Except when it comes to business they believe in all these insane regulations like making sure a work site is safe or not working people into exhaustion for not enough pay to raise a family.
Republicans, on the other hand, are socially very conservative. You're supposed to go to church, adhere to a dress code, just say no to drugs, try not to accidentally be born black, and all these other things. But when it comes to business, they're the ones who are all about freedom! Do whatever you want! Wreck the economy with pump and dump schemes, blast the shit out of whatever nation that has oil you want without asking Congress, don't pay your workers enough to even be able to buy your products, give yourself unlimited CEO bonuses, ruin as many ecosystems as you want and don't even clean up your spills, woo!
The result is that each administration makes things more authoritarian in either the fiscal or social realm, then tags out to let the next administration capitalize off the new bigger government, while it sets to work making things more authoritarian in the other realm.
You may have heard of Libertarians. They pit themselves as "socially liberal, economically conservative", which basically means they believe in just letting everyone do whatever they want wherever they want.
But so the political compass then realizes that "left" and "right" are no longer adequate to describe what is going on. Hence, the political compass uses the traditional left-right axis to plot where someone stands economically (communist vs capitalist), as well as an up-down axis to plot how authoritarian people want their society (anarchy to totalitarian dictatorship).

Interestingly enough, Trump took advantage of all this. Hillary was pitted as being in league with the giant megacorps everyone is beginning to hate as the new corrupt authoritarian Power Elite.
Which, she is.
They all are.
Trump somehow (I think he's the richest person to ever take office?) managed to convince the populace that he was the Washington Outsider, commoner Mr. John Doe Q. Public You-Could-Have-A-Beer-With who was going to dismantle the evil Power Elite and bring prosperity back to us commoners.
Okay except that so far he's done nothing but appoint super rich dudes with ties to megacorps like Exxon-Mobil and Goldman Sachs - companies far bigger than the scary Microsoft and Amazon and Uber and Monsanto and George Soros stuff you always hear Trump supporters on a tizzy about.

So really, Democrats and Republicans aren't so different. Check out the political spectrum website, or do some digging into Political Science and History.
Both parties have been gradually drifting more right wing and more authoritarian over the decades, and are closer to one another now than ever in history.
They are both shills to the Oligarchy of Big Businesses who run this country.

I do encourage you to make up your own mind. If you can't think of anywhere else to start, politicalcompass.com has a great test where you can answer dozens of questions about how you feel on the issues and see which candidates you are closest to.
I also encourage people to check out isidewith.com's quiz.
Both quizzes can be quite comprehensive. You can answer as many or few questions as you want, but there are a lot of questions if you do the whole thing, plus short explanations of what the issues are about in case you are unfamiliar or have no opinion.