Well you can get general info on what will be scanned depending on the sensitivity of the scan (Quick, Standard Thorough) and the area to be scanned (Local disks, all HDD partitions, Removable Media, floppy or CD/DVD drives and Folder Selection, you choose what to be scanned) from the help file. Those areas which are to be scanned are then scanned according to the sensitivity and if archives have been selected.
See the, Simple User Interface section of the help file, Working with avast! 4 in the Simple User Interface, see image extract.