You can dematerialize and materialize, thus suddenly disappearing only to reappear later at an opportune time.
You spend a 3-shot action to dematerialize, effectively disappearing from the story. You go wherever it is you spend your time "off'', and cannot be affected in any way, except possibly with Summoning: Invocation.
You reappear at the gamemaster's discretion, usually at the end of the scene or fight when you dematerialized. You have no direct control over this, though you can specify an event, place, person or item as an "anchor" that acts to draw you back. Examples include avenging ghosts that appear at the scene of a rape or haunt the wearer of a sword.
Dematerialization can be used to overcome travel obstacles: it is hard for a golem to walk onto an airplane, but when your pals go to New York city, you can dematerialize and then conveniently materialize when they arrive. You can only appear as directed by the story, but as long as you are willing to surrender control to your gamemaster, this is a sort of teleportation.
Where you spend the time between materializations is largely irrelevant. Perhaps you go to the underworld, perhaps you become astral or step out of the time flow. The GM might design special scenarios in this off-world, but don't count on it. It can be cool to role-play the effects this in-between place has on you - it might be scary, paradisical or just wierd.