with $20 is not much choice, but there may be several ways such as trade altcoins or gambling.
Gambling is not a way of earning coins, it is a means of losing coins.
The best way is to just hold on to your coins.

I don't understand why so many people are suggesting gambling as a way to make money. i guess people are lazy and they don't want to work for their money. Rather they prefer to risk it on a game of chance where they could loose their money. In other words, not a good idea.