This is a simple question so I am not going to drag it out very far.

But I was reading something on bass solo-ing and it said I need to
make sure I am in the right key with the guitar.

How do I know if I am?

What are the keys? Etc...

Can anyone explain keys for me?
theres some good articles even within this site to help with that. just search on the home page.
Quote by DiMeTiMe

Quote by imgooley
It was such a good suggestion you gave him pi?

yeah, he gave me pi.
Circle of Fiths. Look it up.

Basically, the key signature is the scale that all the instruments are using, but it can only be major or minor. Some keys are linked, such as a major scale and its relative minor (that's three semitones down from the major key's root, e.g C major (3 semitones down from C is A [C-B-Bb-A]) is A minor. They have the same key signature (no sharps or flats in this case). The circle of fiths helps you to identify the key you're in. For example, the circle starts with Cmaj (all the scales are major), which has no sharps or flats, then the next one is a fith up from C which is G, and that has one sharp. And so on. The way this helps you is that if you're soloing in a piece that is in the key of say, E major, you can only use the Major scale (or major pentatonic scale) to solo with. There are more complex scales called modes that can help you solo more creatively and technically, but they're considered an advanced part of music theory and you should concentrate on learning the circle of fiths and its purpose first.