Mostly you don't have to do anything special with Capture once you have it set up. Just operate the console as normal and Capture will show you what would be happening on the stage.
If you use the visualiser a lot, it's very handy to have an external monitor to show it on. Otherwise you constantly have to switch between the workspace windows and the visualiser window.
If you select fixtures on the console, the fixtures will highlight in Capture so you can see where they are in real life.
Capture lets you can see how the lighting will look from any seat in the house. Even if you're in the venue with the full rig in front of you this means you can see the look without having to run all over the venue.
Set up multiple cameras as described in the previous section and you can either click between them or show the 4 standard camera views as a quad split.