A logic gate is a basic building block of electronic circuits. It takes one or more input signals and produces an output signal based on a specific rule.
Q doesn't really mean anything. It is just the system.
"A", "B", "C" refers to an individual "Toggle Switch"
AND : is on, when both inputs are on (1)
OR : is on when at least one input is on (1)
NOT : Flips the input (e.g. 1 to 0)