If you put something up on the wall, you probably expect it to stay there, but if you put a screw into drywall, that is not going to happen. Drywall consists of gypsum, and it won’t hold up to any kind of force, which is why it is necessary to install wall anchors to give the strength needed. Wall anchors come in many different shapes and sizes. Usually you will be able to find a weight rating for how big a load you can put on it.
Naturally, the best alternative is to mount items directly into studs, but many times this isn’t practical, so wall anchors are your second best choice. Once you have chosen the rating of the anchor, you need to drill a hole that will allow the anchor to fit snugly before you insert the screw. Some anchors just expand inside the hole, while others will pop open behind the wall for some additional support.