The number reported in Box 12 of Form W-2 Wage and Tax Statement (code "W") is the amount your employer contributed to your health savings account (including cafeteria plan contributions).
You will need to complete Form 8889 Health Savings Accounts (HSAs).
See Entering in Program - Form W-2 for more information.
To enter the additional information for a health savings account for yourself and/or your spouse:
Note. The amount from Box 12 of Form W-2 will appear on the screen titled Enter Taxpayer's/Spouse's 2020 HSA contributions.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.