I think many beginner musicians struggle with this issue, myself included.
The point is, music is an art, and art is a form of communication, a form of expression. We need a way to share music, so we've came up with this music notation, which is interesting in its own regard, but is not enough to convey emotion, and conveying emotion is the very point of the art.
But what this emotion mean for music is very hard to pinpoint. A much simpler example is in theater. Pick any play, let's say Hamlet, and give it a read. Loudly. You can try learning a passage and saying. You might actually start to believe what's there or not, but you probably look to others like you simply recite something (unless you have some theatrical skills, case in which I recommend you to ask a friend's help for this experiment). The very point of training for actors is to learn to convey credible feelings along with the words they say. And the director needs to make sure everything comes together nicely.
Coming back to music, simply producing correctly every note on the music sheet is not enough. Actually, it might very well be the case that it doesn't really convey much emotion, just as simply reading correctly Hamlet does not make you an actor. You need to act, you need to add emotion to those notes, just how actors add emotion to their words.