This is set up on a Garmin, but most GPS watches will have similar fields available even if they're named slightly differently.
If you set your auto-lap to 1km, these are used to help get consistent splits. For example, you're 500m into your 1km lap. You ran 4:30 pace for the first 250m, and 5:30 pace for the next 250m. Your watch would show:
Lap pace: 5:00, the average
Pace: 5:30, the current
It helps because it gives you an idea of whether you need to speed up or slow down to hit your pace target for that split. In the example above, if your target is 5:00, you know you need to speed up, you're already at your average pace but currently running 5:30.
Most likely you will need to slow down though, because you're running too fast!
This page is more the bigger picture of how your day is going, how much vert have you ticked off, how much sun have you got left, and what is your average moving pace for the whole event, just to have an idea.
All these are just suggestions, have a look at all the fields available because you may have other data, maps, or compass if you load GPX files. If there's extra pages you don't use, just delete them so you're not cycling through clutter.