How does the state switch happen?

Question

Electronics

Log 1 goes to R1, how then does the signal go to log 0?

Answer 1

when you give a signal - the transistor closes the circuit to the ground - and the ground is 0. What's incomprehensible here?
Imagine that instead of a transistor there is a button, but it is pressed when log 1 arrives, and R1 and R2 limit the pressing force.