What do the keys C, B, M B and M on Canon 60D camera mean?

C is the user setting, you set the shutter aperture iso and other data that you commonly use in this mode. As long as you switch to this mode in the future, it is the shooting data you set before.

B is door B, that is, you can always press the shutter to achieve the purpose of long exposure.

M is full manual mode, and all the shooting data of the camera are subject to your command.