Income tax filing

[Spacy]

I'm new here and not understanding the tax filing system. I'm now giving private lessons, so I'm taking cash money. Should I declare my income every month? If yes, where can I get the application and where should I send it?
Some people told me that even if you don't have any income, you should file 0 $. Is that true?
Thanks for your answers

[gunt]

you will declare your income on your 1040 form which you file before Apr 15.

[eb5 green card]

Yes, you need to file an annual 1040 return, even if you have no tax liability, you should still file it. The tax system can be very confusing, so if you can afford it I recommend using a professional tax preparer. They are not expensive for individual filers.