Step app
How do I make my watch count my steps all day long
Apple Watch Series 5, watchOS 6
Question marked as
It already does that. Tap on the activity rings (if you have the as a complication) and scroll down.
If what you're actually asking is how to have steps show on the screen all day, you'll need to download an app that has a complication for that. I've used one called StepsApp.