Reporting side gig income on US taxes – simple guide?

So, I diligently recorded all income on expenses with the online service Freee and submitted my combined statement (with regular job income) to the National Tax Agency here online back in March. I have already applied for the extension to submit my US tax returns and have until October 15th to submit them.

WHAT I AM HOPING FOR:

Is there a simple guide someone can give me here or share with me or direct me to that lays out what I need to fill out?
Fwiw, I plan to do it all on paper as online options were just making things harder, but I am sure that doesn't change the relevant paperwork anyway.

Thanks so much!