I have been playing trombone for 1 year but recently my band teacher has been having me learn to play the tuba because we don't have a tuba player yet. He told me that its my job to "bring the band together" but I don't exactly know what he means. I know I need to play the right notes on the sheet but if I'm doing that then aren't I already in the band "bringing it together"? I'm not sure exactly what he means...
When your teacher says "bring the band together", he is basically just trying to remind you that the rest of the band is building up from your bass sound. One of my teachers told me that the tuba and lower brass section is like the base of a pyramid, in a sense, because other instruments will follow your bass tone. It's like the other players are just building on top of you, and you hold it all together. So if you sound a little off, then the other instruments won't sound quite right. It's important for all instruments to be playing well of course, but you especially because you're the bass lower tone that "holds together everything" in a sense. That's what my teachers always told me and the other tuba player -- if we ever sounded weird or "off" then they would let us know right away. If you're a solo tuba player in the band then it's even more important; you have a very crucial role. and some very big lungs
Solo voices in the upper range may come in a beat late and catch up, they may play wrong notes and swing back into the right ones and so on. Of course, if it is done accidentally rather than with deliberation and consistency and intelligence, it will be apparent. But they won't be taking the band down with them in general.
Drums and bass don't have that freedom: if solo voices can stray, it is exactly because the rhythm group provides the frame of reference from which other players may stray and return back to.
In other words: the rhythm/bass group does its thing. They have very little leeway to adapt to the others, and that leeway is generally employed "organically", by adjusting the overall volume and articulation, or by gradually adjusting to overall speed changes.
You also don't have the option of playing in a subdued manner until you are reasonably sure of your part. For better or worse, the band depends on you. If you are bad, the band goes down with you. Now the tuba parts tend not to be the hardest and bristling with virtuosity, so with great responsibility does not generally come great difficulty.
But you still have less leeway to "figure out things at the rehearsal" than other players.
In addition, just to clarify a bit, tuba players also are responsible for keeping a strong sense of time and usually play on the strong beats. I would recommend working on looking up from the music in order to stay in sync with the conductor.