Adding to what "ihaveaquestion" said, you should have an icon for your wireless connection in the bottom right corner to the left of the date. It's usually a picture of a PC. Right click on this icon and see you have an option to enable it as it may be disabled. If it says enable then select this option.
Failing that, you may have another icon which will tell you what wireless networks are available, ie. wireless routers you PC can detect. If you have click on it and a box should appear listing networks available in your area. You may get a few neighbours show up as well your own. If your own router is listed simply select this one to connect to. It will probably ask you to enter your security wireless Key which you should have written down somewhere. Enter the key and it should work.