Re: Avast

Providers>>the only ones I run are what applies to this machine.
Which in my case is two.

Scans>>I might run a full scan once a month...just for yuks.
I might run a full scan if I get a smell something isn't quite right.

Some folks will run the scan daily....that's their business....maybe they have a need for that.

"left click" the tray icon, and then select "standard shield" it will show the count of recently scanned files. This scanning is resident, that is, on access.
Avast Home cannot be configured to run scheduled scans - a limitation of the free version, if you want to run a full scan you have to start that manually. The entire computer can be scanned, or just the area you want.
I'd scan once a week, or once a fortnight, or if suspicious. Scanning is recommended with any blacklist based application, because, by definition, the malware signatures are in the wild and infection possible before the security companies can respond to them and add them to the database in the form of updates.
The "providers" relate to the resident shields for each type of internet traffic you are likely to be receiving; instant message, p2p, mail (Outlook express, Thunderbird etc), the standard shield, which scans everything, and the web shield, which takes a peek at web pages you are about to load, and stops any with a known virus/worm.
You can disable any you don't use. (Example, no need to have the provider for Microsoft Outlook running, if you only use Outlook express.)