I built a new home in 1998 since then you can see where the nails that were used to hang the drywall are "popping" out. There are small bumps all over my walls. How can these be fixed?

Also I have some areas in my open foyer where the drywall looks like it has cracked or like there's a seam in it. I don't know if this is where it was taped or what. How do I fix this?

 

Nail pops are best fixed simply by sinking the nail heads with a hammer. It'd be great if you had a drywall hammer, but don't go buy one just for the purpose. Push against the drywall firmly with one hand and drive the nail with the other (with a hammer, of course, not your hand). Just takes a small tap, idea is to set the nail against the drywall, not drive it into the drywall. Patch the indentation with vinyl spackle compound. Spot prime and paint.

Fracture repairs in drywall are controversial. As your home is only 2-3 years old, I'm guessing that it may be moving with the fractures a result. Could be that the cracks are occuring on seams, which should be re-taped and textured. Stress fractures can be repaired by cleaning the fracture of dust, mist it with water, wait a few minutes, then fill completely with lightweight spackle (other spackles are acceptable, but lightweight is easy to use). This sometimes is a permanent fix, but if the house is shifting it'll be more temporary. To me it's acceptable as any repair method will likely be temporary until the shifting has been resolved.

Good luck,
Sonnie