Everything must be set up correctly...
The receiver must put out PPM on the wire you are using and the FC must be configured and wired to receive PPM on the correct pin in the correct FC port. The connection is almost always a single, 3 wire cable from Rx to FC.
Similar for PWM, but PWM requires at least 7 wires. Typically 5 cables/connectors with 1 to 3 wires each. Rx must be configured for PWM in some cases, you must connect the wires to the correct place on the FC, and the FC must be configured for PWM.
Also, you must have a BEC (maybe built into the ESC) and the flight battery must be plugged in to power the BEC which powers the FC and thus the Rx. USB does not power the RC Rx.