First, just in case some people don't know, the power bar is the thing with all the plugs on it, that plugs into the wall. The pieces of your computer (the computer itself, the monitor, a printer, a scanner, etc.) plug into the power bar, to get power. Most power bars also have a red light on them, so you know it is on (and that it has power in it).
Your power bar should have a "surge protector" in it. On the box that it came in, it says if it has one, and it probably also says on the power bar itself.
The "surge protector" stops very fast fluctuations in the power. These fast fluctuations have no effect on most appliances, but they can cause problems with your computer. They can cause it to stop working for the moment, and you will have to turn it off and restart it, and you will loose any unsaved work you were doing. These fast power fluctuations can also cause physical damage to your computer circuits, which will require repairs. So make sure your power bar has a surge protector in it. A power bar sold in a computer store should have a surge protector in it, but some power bars sold in hardware stores do not have a surge protector in them (i.e. they are not really for computers). If you are not sure if your power bar has a surge protector, talk to the place where you bought the power bar.
If you are connected to the Internet through a normal phone line, your power bar should also have "telephone line suppression" (also called "TLS"). Power bars with TLS have two phone jacks on them (some times these jacks are on the top beside the power plugs, but sometimes they are on the end, where they are not too obvious if you don't look for them). One of the phone jacks connects to the phone jack in your wall. The other one connects to your computer (into a part called the "modem" - the modem is a circuit that connects your computer to a phone line).
If you connect your computer directly to your phone line (not through the power bar's TLS connectors), power surges can come through your phone line. These surges can cause your computer to stop working temporarily, or cause more permanent damage. So, if you are using the Internet through your phone line, it's also very important to have a power bar with TLS.