Mollies are
drywall anchors.
They look somewhat like a
really big screw with deadly
flanges mounted on the drilling end. Mollies also (
and this is the important part) have a
threaded hole in their head which allows them to be
screwed.
If you live in a ghetto fabulous apartment that's nothing but a sea of drywall as far as the eye can see, Mollies just might be your best friend.
Your only other viable option for mounting anything on your walls is to buy a stud finder and mount directly into the studs of the walls.
...Depending on how really ghetto fabulous your apartment actually is, you may find those studs few and far between, and unless you're building shelves or something else large enough to cover more than one stud, you might not even have enough support from the studs to do you much good.
So you buy yourself some Mollies.
Although Mollies look a lot like screws, they aren't really. It's better to think of Mollies as portable holes. Portable load bearing holes would be more accurate, since you can put a hole in drywall just about anywhere and just about any time... it's just not going to hold any weight.
How to use Mollies:
One last word... Mollies don't really come out of the wall
very well. Once they're in place, and
you no longer love them or need them, it's really best just to
putty over them and then paint the walls again. Removing a Molly leaves a hole in the drywall about the size of a
dime, which
landlords rarely like. And of course you're dealing with landlords, cause surely you didn't
buy anything so
ghetto fabulous, right?