Donations from Ko-Fi

So I'm an online artist and didn't really do commissions till this year. However, last year, I did have a Ko-Fi account which accepted donations. I wasn't really advertising nor encouraging people to donate. My friend found it and gave me $15 dollars. I was wondering which form I would have to fill out or if I have to fill one at all. 

 

Note: I haven't really used the money for anything, especially things that would help me make newer profits.