How can a beginner start trading?

It`s difficult to say, because each of us has his own vision.
I prefer to choose practical ways, rather than just theory.

I guess you can learn theory and try yourself as introducing broker (https://justforex.com/partnership/introducing-broker/?afm=152b31), where you need to promote a broker service and attract trader to start trading with them. It`s a nice way, since you have no expenses, but you even earn some money while studying.
A high commission for your work is an additional motivation for you:

• up to 5$ on ECN Zero
• up to 10$ on Mini and Standard accounts
• and an extra 500$ each month

At the same time you can start your trading career on the Cent and then on the Mini account, where you don`t need to deposit huge sums.

So take theory, add practice and you will get nice result and high profit.