”Walls are Made of Two-by-Fours, Right?The main type of lumber for walls is the 2x4, also called a stud. These studs are mostly arranged vertically.
“I Know that Walls are Either Load-Bearing or Non Load-Bearing…”Yes. And there are no exceptions to this rule. A load-bearing wall supports the weight of the house above it; the non load bearing wall supports only its own weight.
"How Far Apart are the Studs?Non load-bearing walls can have vertical studs spaced as far apart as 24 inches on center. After all, why not? They are only supporting the weight of drywall and some electrical and plumbing work within. Load-bearing walls are quite a big deal, and codes take them seriously. This (mainly) predictable spacing lets you easily find studs when trying to hang a shelf. Generally, load bearing walls have studs spaced at 16 inches on center. Also, headers are shorter.
”Headers? What Do Headers Do?”Headers are those horizontal members that run across the top of doors, windows, entryways, etc. Headers are important because they support weight that ordinarily would have been supported by vertical studs in that space.
The reason you should care about headers is that they give you air and light. The wider the header above the window, the larger the window. Thus, more air and light. Also, within the house: a sturdy header above the door between kitchen and living room can help tie the two rooms together.
”Can You Remove a Non Load Bearing Wall without Taking Extra Precautions?As for structural precautions: generally not. However, you need to realize that you must be careful in case live electrical wires or plumbing run thorough. Non load bearing walls are sometimes called partition walls. Over time, previous homeowners may have foolishly added features to the house which use the partition walls for support.
Even though they should not have done this, you need to be aware of this and not assume that all partition walls are not bearing weight or providing some kind of sideways strength. This is the point where I issue a word of caution: before removing any wall, consult a licensed contractor or structural engineer. Even the pricey fee for a structural engineer is far less than the cost of repairing a collapsed roof.