I’m currently a sophomore and I started a small art business/company where I sell my paintings and such online. It takes up a large chunk of my time and I do make a decent amount of money for what it is, but how would I prove this to colleges? All I have is a website. I am unfamiliar with the application process and I’m not sure where/how you would put an EC like this on your app. It’s not like a school club, where colleges could call up the school to verify. With less verifiable ECs, do they just take your word for it?
They take your word for it and occasionally may check.
You should talk to your counselor about this. If activity is significant to you, have your counselor include it in his or her recommendation letter.
You put this in the activities section of the Common App.
Agree with the above, and I also think this is a really good EC so you should prioritize it over others, especially if you spend a lot of time doing it. You want to catch the eye of your app reader right away, and this is much more interesting than an after school club or similar.
Are you also submitting a portfolio? If so, you should familiarize yourself with various college’s requirements for doing so. Some colleges specifically say they won’t look at manga-type Art, for example. Others say they will only look at juried art works. Some colleges have a specific online supplemental submission system which you have to pay for before you can upload your stuff to it. Forewarned is forearmed.