Well, your CV has 4 slots for different aircraft types, scout, fighter, torpedo bomber and dive bomber so make sure you have the right one selected before trying to put planes in a slot.
You'll get a simple window with a list of available aircraft, similar to how you load ammo. Select which plane and how many then click ok. If you load bombers, dont forget to then find them and load them with weapons, identical to how you load ammo into a gun. The amount of bombs you choose is the total available, so for example 10 bombs would only allow the first 10 bombers that take off to have any bombs, they still only carry 1 each.
I don't know which stage of the process you are getting stuck at, that would help.
Also, I hope you know you will need a total of 8 pilots for when you reach lvl 120 and the sooner you start leveling them all together the better. This is often missed by most new CV players.