There are a number of different kinds of mounting systems. These are all listed above. The panels need to be attached to a structure in some way, shape or form, right? That's what a mounting system does. It attaches the panels to the structure they're mounted on.
Types of Mounting Systems
Roof Mounts
Roof mounts come in a few different forms, but they're all fairly similar. Most are made out of aluminum and fasten into the rafters of your home, through the shingles. There are effective ways of getting your roof mount not to leak. The most effective way of accomplishing this is to use flashings for every lag screw that goes through your roof to support a rail footing.
For the most part, the average roof mounting system is essentially connected directly to your home without much leverage in your ability to tilt the panels in any particular direction. You can install tilt mounts on a shingle roof, if you want, and the result can sometimes benefit your annual production. But most people don't install tilts on their homes, even though it's possible, just because it can look something awful.
Flat Roof Tilted Mounts
Most mounting systems that are designed for flat roofs utilize a counter-ballast system. Meaning? Blocks of cement are usually used to keep the mounting systems on the roof in the event of high winds. The rails are connected to trays which hold the blocks.
Ground Mounts
If you've ever seen solar panels out in a field, they're ground-mounted. It's sometimes the same stuff that is used on residential mounts (in fact, all of these rail mounting systems are very similar in the ways that the panels attach). Ground mounts are connected by pouring cement into cylindrical areas around the footings. 
Pole Mounts
Pole mounts are different from ground mounts, in the sense that they can be adjusted easily. They contain a part called a "mast" which goes to a series of rails that can hold usually 12 or 16 solar panels.
Some pole mounts are able to track the sun, meaning that motors and sensors make it possible for the array to face the sun at an optimal angle all day. This can have as much as a 20% improvement on the overall production of the system.
Research
Unirac Mounting Systems
WattSun Solar Trackers
