Mixes are not required for basic 3 or 4 channel operation. Neither are Rates.
Assuming Mode 2 (Throttle and Rud on the left stick)...
For a 3CH plane
Ail ... RX CH1 controls the rudder servo...yaw and roll
Elv... RX CH2 controls the elevator servo...pitch
Thr ... RX CH3 controls the ESC
For a 4CH plane
Ail ... RX CH1 controls the ail servo...roll
Elv... RX CH2 controls the elevator servo...pitch
Thr ... RX CH3 controls the ESC
Rud ... RX CH4 controls the rudder servo...yaw
A basic muti-rotor is like a 4 CH plane
For a plane you may need to reverse servos to get the servo to move the control surface in the correct direction. You may want to set servo limits (travel limits) so you servos cannot move the control surfaces beyond there physical limits and damage them.
Rates allow you to reduce the amount the control surface can move when you move the stick its full travel. Dual rates let you have two options so you can switch in flight.
On a 4 CH plane you might want a mix to give you a bit of rudder when you use the ailerons...This is to correct for adverse yaw. You also might use a mix if you want to go to 5 channels and have separate channels for each aileron instead of controlling both with one servo.
On a multi-rotor you wont need any mixes
If you are having connection problems then its possible you program is not uploading properly. I might try a new programming cable... they are reasonably inexpensive...
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=41716