Apple Watch and I mac

The Apple Watch can "Unlock" your Mac, if you set it up to do that.

The Apple Watch can "Authorize" some Mac features when you would have normally had to enter your password to enable the feature (this part is not consistent, but when it works, it is great).

For the most part, that is the extent of the Apple Watch and macOS interactions. Then again, I may have forgotten something.

the watch requires an iphone a mac is not enough, a watch can be used to login a mac computer if it's new enough to support it