A 35 mm SLR camera is probably the most popular type among people who are interested in taking more than just "snapshots". If you just want to take photos of your kids, vacations, and family reunions, and don't want to hassle with a bulky camera and some complexity, get a 35 mm so-called "point-and-shoot" or an APS (Advanced Photo System) camera. For $200 or $300, you can get a fabulous camera that will fit in your shirt pocket. For a lot less, you can still get something that works extremely well.
What is an SLR system?
The main advantage of an SLR camera over the point-and-shoots is that you can change the lenses so you can have exactly the right lens for the subject you're shooting. (Of course when you're in the field, the right lens will always be the one you left at home because it's too heavy, but that's another story.)
"SLR" stands for "Single Lens Reflex" and "DSLR" stands for "Digital Single Lens Reflex". When you look through the viewfinder, you actually look through some prisms and mirrors, and you wind up looking through the lens. When you trip the shutter, the mirror flips out of the way, and the scene that is projected on the film is exactly what you saw through the viewfinder. If you put on a different lens, you automatically see a different scene through the viewfinder.
The "35 millimeter" refers to the width of the film. It's certainly possible to make an SLR camera that shoots different-sized film, but they are fairly rare. The DSLR cameras usually do not have a sensor as big as 35 millimeter film, but most use the same lenses.
There are a bunch of advantages of SLR cameras over the more compact point-and-shoots:
• You can expand your system to match your interests. If you suddenly get interested in photographing tiny bugs, just get a macro lens, and you're in business.
• Upgrading is easy. If a fantastic new camera body comes out, you can replace your old one, and all your old lenses will continue to work.
• Backup is easy. If you're going on that once-in-a-lifetime safari to Africa, take two bodies. If one fails, you're still in business.
• Almost every level of equipment quality is available -- you're limited only by your pocketbook. With a point-and-shoot, you get the lens and flash that comes with your camera, and that's it.
There are some disadvantages as well:
• SLRs will be heavier and bulkier than the point-and-shoots.
• SLRs will probably cost a bit more.
• Most point-and-shoots are optimized so that any idiot can use them. This is not necessarily true for SLRs
• The fact that the mirror has to flip out of the way just before each shot means that the actual photo is not exactly what you see through the viewfinder -- it's what's there a few hundredths of a second later. Usually this doesn't make any difference, but if you're photographing rapidly-moving objects, it can.