It depends on the application. Toggler makes SnapToggle bolts that hold up to several hundred pounds per anchor, provided there is a big-enough space behind the drywall to install them. These are about the most durable and highest test load you can find. Other anchors (Toggler SnapSkru and others) will hold a bit less but don't require as large of a channel behind the wall.
No, you don't use drywall anchors if you can use a stud.
The drywall anchors are designed to prevent any damage to the walls. This is the best way to install these shelves without any damage at all.
Drywall anchors should be placed no more than 16" apart. On a 20 foot wall you should place approximately 15 drywall anchors.
You cannot just hang LED TVs on the wall with screws alone. The screws will pull out of the drywall and the television will fall to the ground. To keep this from happening, you need to use wall anchors instead. These are made of plastic, and you can put them into the drywall. You can then put the screws into the anchors. This will make sure that the weight of the television does not cause it to fall.
Screw anchors are used when a thin screw won't get sufficient support from the surface it's screwed into. - Drywall, for instance will not generally support thin load bearing screws, so this is a typical case where you would use screw anchors.
If you are attaching it to drywall, use plastic anchors with the screws. The anchor expands while the screw is being installed and helps hold the fixture firmer to the wall. If the fixture is kind of heavy, use a "butterfly" anchor (the hardware store clerk will know what you want). Butterfly anchors open up like a butterfly's wings behind the wall as you insert the screw.
Drywall anchors are small devices used to hold heavier items you plan on placing upon walls, especially if you don't plan on using the studs. You typically drill a hole where you plan to mount whatever it is you're mounting, screw the drywall anchor in, and then place the screw inside the anchor. The drywall anchor will hold tight to the wall so things don't fall or ruin your wall.
The instructions in the box are usually decent. Just use plastic anchors for the track screws in vertical drywall surface. IF IT"S OVERHEAD mount-use the anchors that spring open once they go thru the hole for safety. Lights pretty much slide on the rail.
It is possible to use VCR mounts on drywall. Some VCRs come with mounts specifically for use on drywall. In the long run, however, it is probably best to secure the VCR mount on a wall stud, rather than just hanging it on the drywall.
If the wall is made of drywall/sheetrock/gypsum wallboard, use one or more screw anchors. This is a plastic cone that comes with a screw. You drill a hole, push in the plastic cone, and use a screw driver to thread the screw into the anchor. Typically the instructions are on the package of screw anchors. Larger anchors will hold more weight, but the size of screw anchor you can use is limited by the thickness of the drywall, so the thickness of the drywall limits the weight it will support. It might be possible to use multiple anchors, but that might require some calculation and planning. If the wall is not drywall but plaster and lathe, you can use a lag bolt. This is a long threaded rod with a spring-loaded folding wing-like thing that threads on the end. To use it you drill a hole large enough to accommodate the folded wing. Push it through the hole, and the wings expand and grip the inside of the wall. Turn the screw to pull it up tight. For a brick or stone wall, there are special masonry drill bits to drill a hole, and anchors of plastic or metal that go in the hole. These expand to grip the wall when a matching screw is driven in. If the wall is not too thick, you could use a lag bolt like above. For a wood wall, simple wood screws should work. For smooth tile or glass, consider any epoxy adhesive.
Extremely easy. All you will need is a level, a drill, and some screws. If you are mounting to drywall make sure to use dry wall anchors.
You use scrap pieces of drywall and joint compound.