Age doesn't matter for taxes. You pay tax on your income no matter your age. If you are under 19 on Dec 31 someone like your parents can probably claim you as a dependent. If you are over 18 but under 24 and a full time student they can still claim you no matter how much you make.
Your employer fills out the W2. The W2 is to report the total amount they paid you and the deductions for the year. You enter it into a 1040 tax return. The 1040 is for the federal government (the IRS). Your state will also have their own tax return. You fill out the tax returns and send the 1040 to the IRS and send your state return to the state. As I said just wait and see. Your first year should be simple to do. Good night, it's getting late.