"can i connect more than 1 servo in 1ch in the receiver? "

Yes. Typically both aileron servos will plug into ch. 1, using a "Y" wire harness. The same is true for two ESC's (if twin motors) both connected to ch. 3, again using a "Y" wire harness. The rudder servo and nose wheel servo also will plug into the same channel, again using a "Y" harness

"the motor i'm interesting in is working with 22.2v battery but everything else with 7.2v, what i can do to combine them?? is it possible?? "

Yes, it is possible to use a 6S (22.2 v) battery for the motor. But you will have to power the receiver separately. You can do this by using a separate voltage regulator, sometimes referred to as a UBEC (universal battery eliminator circuit) which takes power from the 6S flight battery and regulates that voltage to a level suitable for the receiver. Or you can power the receiver with its own small battery.

"why the ESC is needed?"

The ESC is used to convert the battery supplied DC voltage and current to a form that can be used by the motor as well as control the motor's speed. If the motor in question is of the brushless design, the ESC must be designed for that application and will have three wires going to the motor. If the motor in question is of the brushed variety, the ESC will have only two wires going to the motor. If the motor is a brushed type, you could connect the battery directly to the motor but you would not have any control over the speed at which the motors shaft turns.

The ESC must be designed to handle the voltage in question as well as the maximum amperage the motor is expected to draw.