I use foundation for most of my face, and just use my foundation-matched concealer for under my eyes in most cases. I use color correcting concealer to cover up beard shadow (upper lip, lower lip, chin/chinstrap). Before I had much laser, I needed to use an orange color corrector, but after my laser sessions I now just need a peach one (I still generally apply two layers on the top lip). Some people use concealer for contouring, but I prefer sculpting sticks. I have fair skin with cool-neutral undertones, so I generally use the Wet'n Wild megaglo stick since it's very affordable, although for a lot of the dark contour I like to use the Essence Baby Got Bronzer in Moondust since it's one of the few cool toned contour products that i've been able to find.

JohnBrownsBussy2 gave a lot of great detail. The only thing I'll add to her comment is that I put some around my nose because I get a bit of redness from allergies. I'm lucky to have fairly even toned skin, so I don't use foundation with it. The downside of that is it limits how much you can layer over any facial hair shadow without it looking caked on, but that might be a skill issue for me 😬

Depending on how much you use, you might find you don't have much color in your face. I have found that adding some blush can bring that back and make the concealer much less noticeable.