Cerberus in Chains

What does 'your location' mean?

In this case, 'your location' means 'a location that your avatar occupies.'

What does 'can't move itself away' mean?

Cerberus can't choose to move to a location that is farther from your avatar than its current location. (Count distance using steps that Cerberus would take using its own modes of movement, e.g. Airborne if it gained it somehow.)

If your avatar occupies a site you don't control, can you summon Cerberus there?

No. The first sentence is an additional restriction on summoning.

How does Cerberus in Chains automatically follow you?

Whenever your avatar enters a new location, teleports to that .