Suspension is in most cases not the first response to misbehavour by a user. The first steps are contacting the user and telling them what they are doing wrong, this can be formally via a moderator message or informally in a comment or chat message. For serious incidents, this might be skipped.
The guidelines from SE on suspension lengths are
- 7 days for the first offense
- 30 days for the second offense
- 365 days for the third offense
There is no permanent suspension, one year is the maximum generally used (though it is possible to suspend for longer). If a user misbehaves again after a year-long suspension, they are suspended again for a year.
Those are the predefined values available in the suspension dialog, but moderators can choose any other value if they want to.
Here's a screenshot of the suspension part of the moderator message tool: