"Um" is a crucial element in the Chamorro language. It takes a word that isn't going anywhere and makes it go somewhere.
Take, for example, the word "kånta." It can mean "song" and it can also refer to the act of singing.
If you are telling one or two people to sing, you say "Kånta!" It's an order, or a request. But nobody is singing yet. You're hoping they will start to sing, sometime in the immediate future. No action has occurred yet.
But if you want to describe how someone is singing, or was singing, you need the "um."
"Um" is an infix. We know that a prefix goes before the word, and a suffix comes after the word. An infix goes inside a word.
So, kånta becomes kumånta. Now an action has taken place. It went somewhere. Now we need to know who did the act.
If you were the one who sang, you'd say, "Kumånta yo'." "I sang."
If you're telling someone that s/he sang, you'd say, "Kumånta hao."
If someone else sang, you'd say, "Kumånta gue'."
Notice that we've only been talking, so far, about individual people. The "um" works only for one or two people.
So, if you're telling two people that they sang, you'd say, "Kumånta hamyo."
Or, about two other people who sang, "Kumånta siha."
But talk about three or more people, you don't use "um." You use something else we'll talk about in another post.
Notice also we haven't been speaking about action that is going on now, as we speak : "I am singing." We'll look at that later.
AND.....make sure you pronounce "um" in Chamorro....like OOOM and not UHM.