...Using 4$ is wise decision to trade to test out things how it works maybe who knows if there would be improvement while trading over there, even though $4 seemly to be too small but it is a good start than using huge amount to trade and get it swipe off in couples of minutes.
With $ 4, you are unlikely to be able to gain trading skills, since almost every exchange needs to have more deposit to open an order. The right solution for such a deposit would be trading on a demo account, and in parallel with this, finding a job that would allow to collect the necessary deposit for trading on a real account.