I always see these people on PC laying on the ground, sitting anywhere, things like that, is this a mod? or is it just console commands. I wouldnt think its a mod, cuz all the NPCs do this all the time....

If you mean, the PC him/herself laying down or sitting down or have posing/eating animations, mod

But in vanilla game default, NPCs can do these.

Do you know which one it is? Cuz i cant seem to find it.

Yes, there is a mod called "Dovahkiin Relaxes, Too" where you can do these animations. It uses the Power/Shout function to toggle the animations on or off. It's what I use to get the screenshots for my ranger (see sig).