In the lettered blocks on the top left of the W-2 form, you should find your Social Security Number, name, and unit information.
Box 1 Wages, tips and other compensation
This box shows all your taxable income. If you have tax-exempt income, it will not be included in this figure.
Box 2 Federal income tax withheld
This box shows the total amount you had withheld for payment of federal income taxes. Withholding is calculated based upon the instructions that you gave when you filled out your W-4 Employee's Withholding Allowance Certificate, or when you entered the same information into the MyPay withholding instructions page. To better understand withholding, read What Is Income Tax Withholding, and Why You Want To Get It Right.
Box 3 Social Security wages
This is the amount of your income that is subject to Social Security Taxes. For most people, this will be the amount in Box 1 plus the amount in Box 12, Code Q (if any). Income earned in combat zone tax exclusion areas are included in this amount. You are only taxed on the first $113,700 of income each year, so if your income exceeds $113,700, then this box will only say $113,700.
Box 4 Social Security tax withheld
This amount shows how much Social Security tax you've had withheld during the year. It should be equal to 6.2% of your Social Security wages shown in Box 3.
Box 5 Medicare wages
This is the amount of your income that is subject to Medicare tax. This should equal the amount listed in Box 1 plus the amount listed in Box 12, Code Q (if any.) Income earned combat zone tax exclusion areas are included in this amount.
Box 6 Medicare tax withheld
This amount shows how much Medicare tax you've had withheld during the year. It should be equal to 1.45% of your Medicare wages shown in Box 5.
This box lists a wide variety of important figures with codes next to them for identification. The most frequently seen codes on military W-2s are AA, D, and Q.
Code AA represents Roth TSP contributions. The AA will have a number next to it that designates the tax year for which the contributions were made.
Code D represents traditional TSP contributions. It can also have a year code.
Code Q indicates income that was earned in a combat zone tax exclusion area. You may elect to use this amount for inclusion in calculations for certain tax credits such as the Earned Income Credit.
Box 14 also shows miscellaneous other figures. The most frequently seen code on military W-2s is code E.
Code E represents traditional TSP contributions made with income earned in combat zone tax exclusion areas.
Boxes 15 through 20 include similar information for state and local taxes.
It is very important that you check your military W-2 against the information contained in your own records and in your 2015 Leave and Earnings Statements (LES.) You would be surprised how often military W-2s are wrong. One year, my husband received several amended W-2s before we actually got the right one. If you think you spot an error, start with your unit's finance folks. Amended W-2s must be issued by the Defense Finance and Accounting Service (DFAS.)
If you have more questions, please ask in the comments. If I don't know the answer, I'll try my best to find out!