How do I prove to colleges that I self studied coding and can I out it and an extracurricular?

Applying to College Common and Coalition Application
1

I’ve been coding for a year now ( not very good at it but for the next two years I’m planning to expand my knowledge)
How can I prove to colleges that I self studied coding and how do I make it look good?

2

The best way to convey this information in your essay. If this is something that you want to pursue further and it excites you, express it in your essay.