You take your normal action for the round at the time that you manifest this power, rather than waiting for your turn to come up in the initiative sequence. In subsequent rounds, your place in the initiative order does not change—you anticipate your action for this round only. You can take a standard action and a move action, or a full-round action, just as you could if you were taking your action at your normal place in initiative order. You can't activate this power if you're flat-footed, and you can't use the power a second time until after your next turn has passed.
For example, if you normally act on initiative count 15, you could use this power to take your turn again on initiative count 12, but this means that you wouldn't be able to act on the next round's initiative count 15 (since you've already used that turn's actions), and you wouldn't be able to use the power again until after your next turn (that is, after the next round's initiative count 15).
If you spend 2 additional power points, your place in the initiative order changes, much as if you had delayed (but you may move earlier in the initiative order rather than later).