Hello
I’m new to avast and just wondered what is avast rootkit used for, i have recently got avast 4.8 home edition and i think its alot better then AVG 8.0 which i had before avast, but wanted to know if there is anything else i should be using with this AV. 
TY
Hi and welcome!
avast! scans for active rootkits automatically a few minutes after system startup. It can be toggled on/off in Program Settings > Troubleshooting.
Inactive rootkits are detected by signature as part oif the standard scan or by the Standard Shield if they are executed.
See rootkit definitions:
http://www.google.com.br/url?sa=X&start=1&oi=define&q=http://www.f-secure.com/security_center/malware_code_glossary.html&usg=AFQjCNFJ22Hs59orMQQ0TfyxOAasJtcirQ
http://www.google.com.br/url?sa=X&start=3&oi=define&q=http://www.compukiss.com/techionary/212.html&usg=AFQjCNGg6Pr-69VCbzXIfLaVmMvCEHOhTQ
http://www.google.com.br/url?sa=X&start=4&oi=define&q=http://www.softsphere.com/online-help/defensewall/source/information_security_glossary.htm&usg=AFQjCNFi7_SCHpAzWvdcKBdVvkyEGHXL6w