They're actually pretty handy and have decent AI.
They automatically take off whenever you fire your weapons, and automatically seek out the nearest target. If it's a sub, they basically just circle overhead. They have to be stored on the same level as the runway, and they can automatically get themselves to it in order to take off.
More runways are helpful because you can pump them out faster--6 runways can clear 36 planes in 6 waves, compared to 9 waves for 4 runways or 18 waves for 2 runways. This is especially important if the opponent has Mk45's and closes quickly--if you only have a few runways, he can concentrate his Mk45 fire there, and stuff all your planes as they come out. With 6 or more, he'll have a lot more trouble and will probably miss a few.
Fighter planes have a limited supply of rockets, but when that's out they'll still circle the enemy and use their machine guns. They have unlimited machine gun ammo. Torpedo planes are easy to shoot down, they come in low and direct. But their 4,000-hit torpedoes can be fired from 2.5km away, and those are hard to see. Dive bombers have to fire from point blank range, but they're hard to shoot down once they've flown high enough. Then, as expected, they dive down to hit the target.
Your odds are 20-40% for any individual plane to get a hit, but any more than 2-3 hits and you stand a good chance of damaging their engines. Without speed, they'll have a hard time damaging other planes or your guns. So while planes alone aren't often enough to sink the target, they're usually enough to tilt the odds in your favor.
Bombers and Torpedo planes have to come back and reload after one shot, if they survive that long. But they don't usually get a second run, since your runway catches fire if it gets hit at all. It takes maybe 30 seconds without a hit to put the runway out, and in the heat of the fight that just doesn't happen. If the planes can't land, they just circle around your boat until a runway becomes available.
I think they did a great job developing things, and I hope BR follows the same suit. They released a basic game with solid features--build a ship, add a gun. Then they made subs a thing. Then, after (presumably) much work, they added planes and gave a great incentive for in-game purchases. They've also laid groundwork for the next release to include jets and missiles--the missiles are supposed to have solid accuracy, and the jets are supposed to have greater attack range and strength. I'm sure they wanted all those things to begin with, but they built a solid base with a solid game and then just added to it.