You MUST tell us the brand of the radio, the receiver brand does not matter as long as it is the same shift. The radio determines channel assignments.

If it is a Hitec or a Futaba:

Ch 1 primary turning surface - usually ailerons (sometimes rudder on a 3 channel plane)
Ch 2 Elevator
Ch 3 Throttle
Ch 4 Rudder
Ch 5 Retracts (sometimes second aileron or second flap servo)
Ch 6 Flaps (Sometimes Second aileron)
Ch 7 Utility (sometimes second Aileron)

Depends on what you are setting up. It would all be explained in the instructions for your radio.

RTFM - read the friendly manual.