Both.Tosspot wrote: I've had my bicycle I think for over a month now, and it's practically unrideable. The chain won't stay fixed on the spoke things. My mom, who used to be into bicycles and fitness before she let herself go, says that this is common with new bikes after a kind of "break-in" period, and that I need to go to a bike shop and get the thing tuned up. Does this sound about right, or do I just have a hoopty-ass cheap bicycle?
Keep in mind that all of that fancy magic is accomplished with springs and cables. The cables stretch out a bit after initial use so the proper tension to match the shifter selection to the appropriate cog might get skewed a bit and need adjusted. A shop will probably just give the barrell adjuster on the back of the derailleur (the springy chain mover thingy on the back) a quarter turn counter-clockwise to pull more cable and make things tighter.
There are also two screws on both the rear and the front derailleur (the cage thingy that moves the chain on the front chainrings) and these screws control the limits that the two springs can travel. Often chain problems are a result of those screws not being set correctly, allowing the derallieur to pull the chain past the last cog or ring. A department store bike is usually not built by someone that knows how to adjust these babies so they are probably wrong and causing you trouble.
If you throw a chain and it seems to jam when you put it back on, it probably means that you are in a gear that is drastically different from the one you've placed the chain back on and the force of the pedal is pushing against the chain laterally. Best bet in this case is to shift to the smallest cog in the back (the highest number, the "hardest" gear) so the derailleur is the loosest and the chain has the most slack to allow you to put it back on. Like Kard said, on the front, you can often shift to the big ring and the chain will right itself automatically. Otherwise, shift it so it lines up with the smallest ring for the same benefits.
If you can't figure it out, I'll ride to meet you at any RCP bar and fix it for one (1) non-swill beer. That goes for all of you fine folks.