Unless it's changed since I last did this sort of thing:

Every quarter you need to file and pay estimated taxes.

Every year you need to file your individual tax form, with your freelancing income minus allowable expenses (be careful here!) in a Schedule C and you'll also need to pay your self-employment tax in a Schedule SE (this is both parts (employer and employee, as the fiction goes) of your FICA (Social Security and Medicare) taxes).