Just to add my .02. A propane torch will take two to three times as much time to reach temp, but it will do the job. Make sure you heat the fitting and not the pipe. As was said, heat from one side and feed from the other. When hot enough, the solder will wick in. Don't feed from the top if you can help it. The solder can melt and flow around but not wick in. From the side is preferred. As for wiping, it serves two purposes. One, it looks better. And two, it removes excess flux, which is corossive and will turn the pipe black.

Also, make sure there is no water in the pipe. Especially useful info on repairs. Even a little water can mess up easiest of jobs. With an acetalene, you can evaporate a little bit of water. With propane, it's almost impossible.

Oh, while I think of it, DO NOT USE 50/50 solder on potable pipes. Most places still allow it on heating systems with backflow preventers. People like to use it because of the lower melting temp. Any plumber worth his salt doesn't even carry it.