How do i measure the distance hiked on my tracks?

You should be able to go to the Map page and select Measure from the menu, then just click on the map. You may just want to save hiking and driving in separate files in the future.

That requires me to set a waypoint every time the trail made a turn.  Isn’t there away to “cut up” the tracks?  Essentially, using the existing tracks on the map, and cutting out the sections that we drove, leaving the hiking portions. 

as an alternative to that, how do you save the driving vs hiking to two different files?  I’m not sure what u mean by that?

I don't know how to cut up tracks within the Garmin ecosystem.

If you're willing to go outside the Garmin ecosystem, you can import your track (they refer to it as a "route") and edit it with this website: https://www.plotaroute.com

If I was hiking/driving a particular Place, I would save each segment as a different track. So Place D1 would be my first driving segment. Place H1 would be first hiking segment. Place D2 would be my second driving segment, etc.

This would turn one large track into several smaller tracks, which might be too cumbersome depending on how often you expect to record. 

GPX files can be easily edited in something like Windows Notepad. You can use this to clip out portions of the track. But that requires you to know what portions to clip. For track points, the GPX file normally contains only coordinates and a timestamp. IIRC, the timestamp is in UTC.

Any application which displays the track will automatically connect the ends before and after the clip with a straight line. This may not be desirable for your purposes.

I don't see why you would need waypoints to measure on the map at explore.garmin.com.

To do this externally use Garmin Basecamp.

To make this information available on the device, each time you change from driving to hiking or vice versa,  save the current track and start a new recording. Then view the 'Hiking' recordings on the device to see all the stats,  including distance. 

Also, to correct someones mistake in another post,  tracks are not called routes, they are called tracks. Routes are called routes.

To correct your mistaken post, I wrote, "they refer to it as a "route"".

The website I linked to calls GPS recordings routes. HamFam calls the recording a track.