By choosing to delay, you take no action and then act normally on whatever
initiative count you decide to act. When you delay, you voluntarily reduce your own
initiative result for the rest of the combat. When your new, lower
initiative count comes up later in the same round, you can act normally. You can specify this new
initiative result or just wait until some time later in the round and act then, thus fixing your new
initiative count at that point.
You never get back the time you spend waiting to see what's going to happen. You can't, however, interrupt anyone else's action (as you can with a readied action).
If you take a delayed action in the next round, before your regular turn comes up, your
initiative count rises to that new point in the order of battle, and you do not get your regular action that round.