Welcome to HW!
I can understand how you feel, and I found that there isn't a simple "knob" to turn. But let me tell you you aren't useless, no one is ever useless, everyone is perfect in their own way. I am absolutely certain there are plenty of things you are good at, it is just easier to neglect those and only see the things you aren't good at. I had plenty of things I was (and still am) really good at, but I felt the things I lacked were the ones that would make me happy. I felt I was good at everything I wanted, but awful and the things I needed. Of course, that ain't true, and it took a while to realize that, but now I do.
Maybe you could write down for yourself, or here on the forum, the things you just can't seem to get right, and also the things you actually are good at. Writing this down can give you a clearer picture of what is going on, what things are letting you feel bad. A major step in getting better is to be aware of the causes.
I hope to hear from you again!
Acceptance is the key
Existential depression and Insecurity
Try to keep smiling! :)