How X10 Modules Work
Most X10 modules work just like remote controlled switches–you send them a signal, and they either turn on and off. Some modules also have more complex functions, like dimming, and some can send signals that indicate whether they’re on or off, but the basic idea for all modules is the same.
In order to determine which module turns on or off when a command is sent, X10 uses a series of House Codes and Unit Codes. These are set on the module itself, usually using dials (some of the smaller modules are set using a combination of button presses and pauses–check the manual if you’re not sure). There are 16 unit codes (1-16) and 16 house codes (A-P). These are combined to identify a certain unit. For example, you could set the unit code dial on a lamp module to 2 and the house code to A. If you sent the command A2 ON using Powerhome, the lamp would turn on. By combining house and unit codes, you can have 16*16, or 256 different modules in a house (assuming your neighbors don’t use HA).
It’s a good idea when installing a system to keep track of which code combinations you’re using. That way you won’t overlap, and if you need to reconfigure your software, you’ll remember which codes go with what. I use Google Spreadsheets to keep track, since I can then access the file anywhere.
Installing Plugin Modules
Installing plugin modules is pretty idiotproof–just plug the module into the wall, plug the applicance into the module, set the codes, and you’re ready.