A 'bus takes or collects a lot of individual things (or people) to a common place, generally with the idea of taking them somewhere else.

Easy right?
In our wold they can also be called 'sub groups or 'sub bus depending on how they're used.
You want to get used to the ideas also of the two signal path choices;
'Iin series' -all of the signal goes through it,
And 'parallel which means your doing a 'split off from the original.
Both are used in combination and in different configurations at the same time-
'Sends imply a volume control for a split off' to one of these 'sub places.
Examples- All of you signals exit your final output at the master bus -series.
Some channels assigned (series) to a sub-bus for a sub grouped common control before going to the master bus.
Some of these channels have 'Auxiliary Sends' to split off (parallel path) some of the signal to a reverb unit that is inserted (insert' is series) on an effects bus' that does master control for the verb and sends it on it's way.
Sometimes there is a master aux send' knob which qualifies it as also being a 'sub-group control.
Then a verb's own
internal mix control can be set less than 100% wet in which case the verb patch is doing it's own parallel thing.. which is what you would do for wet dry control if the verb is inserted on it's own channel instead of on an 'aux/bus path with with the others.
Eq is an example where inserted' on the channel path does its 100% wet' series thing.
Find the flow diagram for your prog', re-read, after a bit it'll come.
