Altitude and Attitude are HOLD modes but they are "passive" (as they don't "fly" the aircraft for you when enabled) and their narrow authority won't e.g. transition a travelling aircraft into a hover - you need to do that manually. Only when in a near-hover state (I believe it's speeds < 5kts) will enabling the Attitude Hold put the aircraft in a controlled hover. I strongly recommend you learn more about these systems as they behave differently depending on your speed and altitude.
Belphe's post in Trim button? was marked as the answer