Above is the way many 3 way switches are wired. This is the simplest. If you have all the white wires (neutrals)tied together, the power is fed to one box, usually by a black wire. Light fed by the other box. The switch chooses between the two ""traveler" wires, which are usually red and black.
Unfortunately not all are wired that way, and if any of the whites were connected to the switches, we really need pics to figure it out.
Below is a simplified view:
