Should I file taxes?

I do have a normal job and file my taxes for that. But I've been babysitting for one family this year and it made me wonder if i need to file taxes for it. I know that if you make a certain amount then it qualifies for taxes. But let's say I made $500 this year just from babysitting and its not my main source of income, how would i even file for that? Does it count as self employed or gig work? It also made me wonder about selling my car and i make 5K from, it would that also be taxed because its over the net earnings amount?