All the C hoses all leak is this suppose to be this way?

These run on pressure side of pump not vac side. Yes the joints leak due to being cheap quality. This system need 4000 to do its job Properly. About four times a year you’re gonna have to pull a part is vegetable oil on anything that moves/rotates otherwise it gets stuck and won’t move the wheels won’t turn properly they won’t swivel properly and you need maximum output to make this thing run properly.

How does it work picking up dirt?

It is NOT a vacuum. It gets hooked up to the pump outflow. It has a "Basket", which is more like a pool screen. It does catch some dirt, but I believe the way it keeps the pool clean is by keeping the dirt from settling on the bottom, and by keeping the dirt suspended, the main pool filter will pick it out.

How to I get the end of hose A to attach to the water return connector? I have a 15' round pool.

There is an adapter that you attach to the hose to. The hoses are supposed to leak a bit at the joints. I've had mine a year and a half and it works fine for me.