Summary[]
Imperium is a progression server. This means that your characters will need to obtain keys to unlock specific zones. Some key fragments can be purchased from Zulu in the Guild Lobby. Talk to Vinz Clortho in the Guild Lobby for information on how to obtain the keys.
Guides[]
Arek from the Imperium forums has written some great progression guides. Eventually they may live here but for now see the following posts. Note that there is no guide for Tier 6 yet.