Framing, or "rough carpentry," is the basic building skill of new construction and almost every remodeling addition project.
Lumber is by far the most popular construction framing material because it's readily available, easy to work with, and comparatively less expensive than other framing materials.
Building codes have a lot to say about framing, because incorrect framing or the use of the wrong materials can have a dramatic effect on the structural integrity of a building and lead to a potentially dangerous situation. Where building is regulated by code, any framing project will require a permit.
For work done under a permit, a framing inspection will be required. Work that does not meet code can be ordered to be taken down.
By itself a single piece of framing is rather weak. It's only strong when connected to the other framing pieces.
If a wall stud or two are warped or not flush, replace or adjust them.
It's common sense, but if framed joints look tight and feel solid the house will finish out better and be more structurally sound.