Depending on the severity of the infraction, a different course of action may be taken, but the usual practice is as follows :

1st rule break (Minor offence)
Corrected, A PM will be sent, no further action taken.
For a more serious offence, a warning will be issued, this is a mark against your name letting us know you have broken a rule.

2nd rule break
Another warning will be issued.

3rd rule break
On your 3rd warning, you will receive a temporary ban, the length of which will depend on the severity of the incident.

On another breach of rules. After this it will be assumed you will not learn your lesson, so you will receive a permanent ban, meaning you will never be able to visit the forum again.