I want to become a professional artist (drawing)... how? Not good at drawing at all...?

You need to GET good to be a professional in the field. This means putting in the time to practice and to learn.

Practice makes perfect!

How many hours a day do you practice basic sketching?

well then learn how to draw? if u cant afford classes theres youtube g luck

Do you need to be professional? It's a hard life being a professional creative, no matter who you are. And if you don't feel like you're any good to begin with, you're mentally at a disadvantage. Can drawing be a hobby or an escape and something else be your profession?

The other thing I can say is that maybe you should try sculpture, instead.

I want to be a gymnast but I cannot do a backflip.

I could exercise, train and learn to do a backflip or I could wish I was a gymnast.

Don't you think you're being unrealistic? You need to set attainable goals.