Please explain box 11 on W-2. I don't understand how to know if I took that amout out.

You took money from a non-qualified plan. You need to discuss this with your human resources department.

The Instructions for Forms W-2  says:

Box 11—Nonqualified plans.

The purpose of box 11 is for the SSA to determine if any part of the amount reported in box 1 or boxes 3 and/or 5 was earned in a prior year. The SSA uses this information to verify that they have properly applied the social security earnings test and paid the correct amount of benefits. 

Report distributions to an employee from a nonqualified plan or nongovernmental section 457(b) plan in box 11. Also report these distributions in box 1