There are only a few plance perked as shown above, you can pretty much fly/drive everything else.
Perk planes are perked just so everybody cant just use them all the time.
When your in a perked plane and stand to losse your perk points if you crash or get shot down you will be less likely to....
take risks
run headlong into a battle wihtout concern for the aircrafts safety
keep upping the same perked plane.
The idea is basicly to limit for whatever reason certain types of aircraft.
The Me 262 for example is perked becasue its a jet aircraft so itll outrun everything else on in the game and the cannons are leathle and just 1 or 2 direct hits will rip an aircarft in two.
You can imagine just how bad the game would get if everyone could up a 262 all the time no matter how many time they get shot down.
other planes are perked are not nessesaarily jets , they just perform well or get used to often.
its there to offer the ability to fly somthing SPECIAL but to also keep the game play in balance.
As said you get points for killing things lol
the more you kill the more perk points you get, you can see your perk point when your in the hanger screen.
a word of warning though.
if you do get enough perk points and want to take out the 262 or somthing else you have had your eye on, make sure you practice offline with it or use it in the practice arena first, you dont need perk point in there or off line, you can fly them NOW.
When you do take out a perk plane remeber that you will always default to the last aircraft you flew, make sure when online that you are not going to spawn in a perked plane if you dont intend too, specialy if the filed is being heavely attacked.
I acidently logged on and spawned into a spitIX plance cos it was the last thing i flew last time i logged on.
I spawned into a airfiled that was being attacked to help to defend it, and got straffed and killed on the runway.
Not normaly a problem but as it was the perked Spit i lost 60 perkies

just make sure what your spawning is my advice lol