Soldering copper pipes is a basic plumbing skill that once mastered will enable you to tackle many DIY home repair and home improvement projects - for instance, replacing copper water lines or installing a new spigot. It can be as much an art as it is a science, thus the more you get the "feel for it," the faster and easier it gets.
Soldering copper pipe, or "sweating" as they call it in the trades, relies on capillary action to create a well-sealed joint. By using a propane torch to heat up the two pieces you are joining, solder is "sucked" into the joint and spreads evenly between the pipe and fitting. Once it cools, you should have a solid, leak-free joint that will last for years.
Use care when working with a torch. Keep the flame away from wood framing or other flammable materials. Also remember to let your work cool before handling it. For step-by-step instructions on soldering copper pipes, take a look at this friendly video tutorial.