What are the letters D in box 12a and DD in box 12b on W2 and do i add those numbers and claim it

Code DD is only information to you to tell you how much your employer spend for health coverage - you do nothing with it.

Code D is the amount of salary deferrals to a 401(k) plan.  You do nothing with than either other than enter it on the W-2 screen in box 12 just like it is on the paper W-2.