I have 20$ of bitcoin. What should i do with it instead of spending all.Tell me Pls.

Using it for trade is not an option, and as of right now, since we don't have to many merchants using it, I don't think there is any reason to spend it. If I were you, I would just keep those coins in a desktop wallet and leave it there. If you can keep investing some more. Since the fees are low again, it's affordable to buy small amounts on an exchange and send it to a wallet.