Hmmm I don't know where to start since you declare as newbie.

WGS84 is the ellipsoidal model of the earth (datum) while UTM is the flat model of the earth (projection). Thus in short your flow of thinking should be like this:

1. Imagine the world - it is not round but shape like an ellipsoid (like a round ball being pressed from the top)

2. Scientist (or mathematician) then assumed (or modeled) the earth as an ellipsoid. There are so many models of ellipsoids and one of them which is commonly used is WGS84.

3. However the map we use is flat hence we need to "flatten" the earth (ellipsoid). There are so many ways of flattening and one of the flattening process produce UTM.

Hope that is clear enough.

Noordin