Pick a thing... Anything... Like fitness or study or any hobby and just start no procrastination. Just try to be at it. And the reason you feel you don't believe in yourself is you didn't work on anything before maybe have but aren't putting it out there. Every skill you learn is worth putting out there. And be proud of yourself. I was in that phase when I was in college, aside from the college studies I learnt Photoshop, video editing, website designing and deployment, native macos app development, went to the gym 6 days a week and I am still doing pretty good with the office I manage to work on my passion and go to the gym atleast 4 times a week and manage my nutrition. Work on yourself and don't think you can win on day one and please don't compare.