Start with something really simple, the voice in your head is going to tell you how stupid it is but ignore it. Try growing a plant it is so simple but can be so rewarding, I don't know if you live in a large city or a small town or in a rural area. Go outside or find just a small pot and put some soil in it. Put a flower in it or a vegetable, what ever you want.

Try watching this video as well it brings me comfort when I'm feeling down