I know what you mean, it was very confusing to me the first time

OK simplyfied version, not all TX RX compo's apply hear throttle position is different on some RX

using a 4 ch RX as an example JR type

ch 1 aileron servo extention plugs in

ch 2 elevator servo extention plugs in

ch 3 throttle or ESC extention plugs in

ch 4 rudder extention plugs in

using a Y haness the 2 female ends will be used for the rudder servo or ESC extention and the batt pack, the male end will then plug into you RX in the proper place

Like I said that is your choice and both ways will work

example on 1 plane I have 4 motors so each ESC has a BEC I have to diconnect the red wire in the harness of each ESC and power the RX and servo's through the rudder connection on the RX

on the other plane it is just a large ESC with no BEC so I use the ESC lead to the Y harness with the batt pack, I unhooked the red wire from the ESC just for precautionary measures and just plug the male end of the Y harness into the throttle on RX

I hope this makes a little more sence