I received blank W-2 form from my employer. What it is mean?

It may be an incorrect W-2 form. If you received taxable wages during the year from your employer, they should be reported in box 1 of your W-2 form. Also, any federal tax withheld should be reported in box 2. Also, typically there are entries in boxes 3 through 6 at a minimum. So, you may want to contact your employer for clarification. 

I only have number under DD.

All taxes were hold as per biweekly statements.

Code DD is the  cost of the health insurance your employer paid for you. If you had wages and taxes withheld, there should be entries in boxes 1 through 6 at a minimum. You need to ask your employer for a corrected W-2 form.

Thank you