Reporting
What can be reported, what happens next, and why reporting a chat message does not copy it anywhere.
Penalties
The four kinds of penalty, exactly what each one blocks, and how appeals work.
Moderation
What the moderation surfaces do, and the limits on them.
The shape of it
Almost everything member-authored on this site can be reported. A report opens a thread between the reporter and staff.
A report may or may not lead to a penalty. A penalty is attached either to a member or to a content item, and what it restricts depends on its type — they are not one ladder. A penalty may expire or may not.
Penalties on servers are a special case: most of them are raised by automated detectors rather than by people, and each detector may only lift its own. See Penalties and Scanning.