There is one chain ring on the front wot you pedal with and one sprocket on the back, hence one gear. There is no freewheel - if you're moving, the pedals are going round, hence the fixed aspect. You stop either by resisting the motion of the pedals with your legs or by using the brake. You're not allowed to race on a velodrome using a bike equipped with a brake but you can fit one if you're riding on the road.

Also the most extreme form of bike porn: www.fixedgeargallery.com

firstly, if you're truely a begining cyclist, would you really want a fixed gear? they're not exactly a safe or easy way to start riding. if you're not experienced and fairly fit, a fixie can be frustrating and dangerous. And I assume you don't mean to race on a velodrome.

Anyway, there's so much to learn....

start with the guru of gears:
http://sheldonbrown.com/fixed/index.html

also the fixed gear forum on roadbikereview.com has many newbie questions and experienced people answering them.

So you slow down using your legs. if you're sane, you would be wise to have a front brake just in case.

The gear is whatever you want. typically a mid to high level one. It takes trial and error to find the right ratio. It has to be not too steep that you can't pedal up hills (if you're riding hills). while not being so easy that you would spin your legs 150 rpms going down hills. And you'd want to go a comfortable speed/cadence on the flats.

therein, lies some of the fun and challenge of riding a fixie: finding that delicate balance between your body and the bike. The gear you take down the hill's gotta get you up it too. The whole single gear situation pushes you to ride cadences both faster and slower than you otherwise would choose on a regular bike. It's not particularly comfortable (duh, thats why they invented multi gear bikes!). You can grind your knees and melt your shorts on the same ride.

as for the bike itself, it is simple, minimal, pure...

i enjoy my fixie so much that i only ride my geared bike (a triple) on long rides with lots o big hills.

track frames and forks are much more rigid and the geometry more upright than a road or touring frameset/fork which has been converted to fixed gear (often considered much more 'practical' in a city). also, it's 'drop outs' (which are really not drops out, per se) differ and the fork is (usually) not drilled to accept a brake.