I am assuming you are talking about the amounts in boxes 2, 4, and 6 of your W-2.

The amounts in Box 2 is for Federal tax withholdings.  When you file a tax return to determine how much (if any) income tax you owe based on your income, filing status, and deductions, the Federal tax withholdings is applied toward your “tax bill”.  If you had more withheld than you owe for the year, then you will get a refund of some or all of the withholdings shown in box 2.  If you had less withheld than you owe for the year, then you may owe additional income tax.

The amounts in Box 4 and Box 6 are for Social Security tax and Medicare tax.  These amounts are paid partially by you by having the amounts taken out of your paycheck and partially by your employer based on the wages that you earned.  You will not get a refund of these amounts.  They are kept by the government to provide future Social Security and Medicare benefits to you.