An exclamation mark (!) inverts a pin. The other symbol (^) enables a pull up resistor on a pin, which is needed for things like endstops or buttons. These can also be combined.
PB0 is just the name of one pin. PC0 would be a completely different pin.
Different Microcontrollers have different naming conventions, that is why you sometimes see names like PB10 and on other controllers it might be GPIO10.
See also the documentation: https://www.klipper3d.org/Config_Reference.html
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