I will be mailing my MacBook Pro for a repair in the mail. Do they need my password to get into the computer? I have done all the other things that the instructions say to do before shipping.

If you made a Time Machine backup of your Mac, I’d do the following:

1. Turn on FileVault (System Preferences -> Security and Privacy) and wait for the drive to finish encrypting.
2. Erase your Mac and reinstall macOS.

IIRC Apple wipes the internal drive regardless if it has data on it or not. The above steps simply ensure that you don’t have to expose your password, and that none of your files can be recovered from the drive.