I have numbers for 12a, 12D, and 12DD. Which number do i add for enter your HSA contributions?

Do NOT enter the code 12 amount for your HSA anywhere else on your return - entering it on your W-2 is enough.

It is the codes that are important in box 12, not the a, b, c, d. HSA contributions are reported with code W.

However, I repeat - once you have entered your W-2, do not enter the code W number anywhere else in TurboTax - TurboTax has already automatically handled it.

Your W-2 may have numbers for the box 12 entries, like 12a, 12b and so on.  These numbers are irrelevant, just placeholders.  The code that indicates what the box 12 item is reporting are single or double capital letters.  A for untaxed tips, D for elective deferrals to a 401k, and so on.   W is the code for HSA contributions, but you should not enter them again later in program.  The HSA is captured automatically from your W-2.  Later in the program, only enter additional out of pocket contributions, if you made any.