What Can I Do With A Legendary Engram?

I completed a heroic public event and in the chest, at the end, I got a legendary engram. It says that it is worth a lot in power levels, but It isn’t something that I am able to equip. What am I meant to do with this? What do you do with a legendary engram?…or any engram I suppose, I am guessing there are rare and exotic engrams too?