It is very simple to install and update. There are really 2 buttons that you should concern yourself with. The Update button and the Scan button.
I highly recommend clicking the Update button and download any definition updates before running any scan. As this is the free version you must run the update manually.
The paid versions will do this for you.
After the update is finished you should click the scan button to scan your pc. There are several types of scans available. The Smart Scan will check the most usual places for spam and spy ware to be install. The Smart Scan runs relatively quick. The Full Scan will check every file on your pc and could take several hours to finish.
Once a scan is finished it will display a screen with a list of items it found. You can simply click on the items and have them removed. If there is something that should not be removed you can add it to the Ignore list.
A nice feature of AdAware is the Quarantine. If you remove something that should not have been removed you can find it in the quarantine and restore it if needed.
Between Adaware,SpyBot Search and Destroy and two others (articles coming) I have restored many pcs to usable conditions.