You link your garmin, apple watch, peloton, whatever to strava. when you complete the workout, it automatically uploads
It also compares your workouts to previous workouts of the same distance/duration/type and the segments portion allows you shoot for personal bests on those segments, and compare your personal bests to others that have run that segment. Unless you are the one creating the segment (which isn't hard) again it's all automatic.
If you're the type who does not need any external motivation, and already track, record, and compare your workouts on your own and that's all the motivation you need, then strava will probably do nothing for you. Also, if you're not the type who cares at all about social media and never uses it, you probably won't use strava either. But I like seeing what others are doing, and when I see that someone else who, for whatever reason, I am internally competitive with has done a workout and I'm feeling lazy, that may be just the motivation I need. Also, it's cool when someone is travelling to a cool location and you see them post a run, hike, kayak, etc in an incredible location (the default post is a map of your workout location, and you can add pictures if you want). For example, several of us did a 25 mile mountain bike ride in Jamaica. It was incredible and scenic, and it's fun for me to still go back and look at it every once in awhile (we took pics along the way too, so those pics are on there and it syncs with your phone so that where the picture was taken shows up on the route automatically)
It's not for everyone, but I personally love it. And for the most part it's just workouts...people call it the "Facebook for athletes" which is BS. It's just people posting their workouts, a few people may comment, but that's it. Nothing else.