You can unlock the Mac by bringing the Apple watch to its proximity. Please navigate to Mac->Restrictions->Allow Device Functionality. Enable the ‘Auto-unlock with Apple watch in proximity’ option to unlock the Mac device automatically without the password when a worn Apple watch comes near the Mac of the same user. Please note that the device will require a password for unlocking it when turned ON for the first time.
This is supported on macOS10.12+
Kindly use the help link of restrictions for Mac devices for further info.