This program does a full scan of your system and shows you all the files you don't need, usually from deleted applications. All the files listed also show their corresponding locations, the space they take up on your hard drive, and the last time you accessed them.
From that list of files, you can select the ones you want to completely delete and the ones you don't think you'll use anymore. When you press the clean button, they will be completely deleted – without going into your trash bin – so you have to be careful what you choose to delete.
The interface also has a shortcut to the selected files' properties and locations, meaning OS Cleaner only lets you clean in a secure way.