You can place your Garrison in several pre-selected places throughout Draenor.  It sounds as though there will be at least one option per zone, and they are preset to prevent players from placing them in sub-optimal places (like a raid zone entrance, for example).

You will be able to move your garrison if you’d like, although we don’t know if there is any cost or penalty associated with it, or if we can only move it every X number of days.