What is this weird green thing that I see in videos on the floor?

When I was watching a tutorial, I noticed that there was something green on the ground and wanted to know what it was, what it does, and how to use it.

This is so vague, lord. I think you’re talking about navmesh

Oh. Thanks!

I’m still new to this

Attaching a screenshot will get you a better answer faster.

you can hit P to enable and disable the visibiltity