There is a ton of information and history out there.
Studs are strong pieces that are the internal structure of your walls. They are covered by some type of material (the "skin") that is what you see when you look at a wall. If you imagine your wall without any type of skin material, there are probably two studs at the left and right edges and definitely two framing members (similar material as studs, but the term studs explicitly refers to the vertical members) going horizontally at the floor and ceiling forming a rectangle. This rectangle has many vertical studs inside of it, usually space at 16" or 24".
A term you'll see sometimes is 16" O.C. which means On Center; it just means the center-line between two studs is 16" apart and there is about 15.25" of air in between them.
Your studs are covered on both sides by something. These days it is typically drywall (sheetrock) which is cheaper and easier to install than most alternatives. Your surface could also be plaster, paneling, tile, etc.
You need to use a stud finder to locate where your studs are because you need to attach heavy objects to studs. Drywall can only support very little weight. To use a stud finder:
- Put masking tape horizontally on your wall.
- Place the stud finder against the wall, holding it vertical.
- Press and hold the button.
- Hold it still for the first half second so it can calibrate itself.
- Move the stud finder horizontally across the wall and mark on the tape where the signal is strong.
- If the signal acts weird, make sure you slide the stud finder sideways at the same height.
- Take a tape measure and try to find a pattern between your marks that is 16" or 24" apart.
- Now you can measure multiples of 16" or 24" and know where other studs are.
You need to determine if your stud are wood or steel because the type of fasteners (screws) you use depend on it.
There are other methods of determining this, but here's one: Figure out where your fasteners are going to go and drill a small pilot hole (smaller than the size of the fastener). If you get about a 1/2" deep and hear a terrible screeching noise followed by your drill bit sliding and having no resistance, you have steel studs. If you get 1" in and you start to see saw dust coming out of your pilot hole and your drill still feels like it's biting at something, you have wood studs.
If you have wood studs, you can use general construction screws (NOT drywall screws). If they are steel, you probably have to use toggle bolts. Toggle bolts are a pain to use, so you can try using self-tapping machine screws with a fine thread first. Make sure your fasteners are long enough.
There are many other types of walls out there so if things don't seem right, maybe they're not typical stud walls.
An over-100-year-old apartment building is likely plaster-over-lath. In that case, you should be able to drill through the plaster and into the lath to sink wood screws. If this is so, you'll see what looks like sawdust on the tip of the drill when you pull it out. I'd probably use a bunch more than just the 4 recommended, but it'll hold a TV under 50 lbs.
If you want to find out what's behind there, just try to drill it (with a drill bit you don't care about). If the tip comes back red and chewed up, congrats, it's brick, and you can sink masonry anchors if you want complete overkill. You'd need to drill with a masonry bit, and then you can choose either expanding anchors or epoxying in something more like a drywall anchor.
This ain't a job for toggle bolts, though.
Best Answer
Attach the shelf brackets directly into the studs, no ifs, ands, or buts. Wall anchors are OK for light loads, but I wouldn't use exclusively them for a floating shelf, even if you weren't putting books on it. I would use at least 2" #8 screws, so you have at least 1.25" going into the actual stud. If your shelf bracket is rather thick, go with 2.5" screws.
If your shelf is short, or you want it positioned such that you'll only hit one stud, you should use wall anchors on the ends in addition to screwing into that one stud. The wall anchors in that case would be more to keep the shelf from rotating. Toggle anchors are certainly appropriate for this case, but the plastic anchors would be OK as well, since they're not intending to support much weight in this scenario.
I like a magnetic stud finder such as the StudBuddy, as it's dead simple to use.