The left stick controls three things. Up and down on the left stick is the throttle and also the "collective pitch", the angle of both the blades as they bite the wind. Down is throttle off and flat pitch (no bite.) Up is max throttle and full bite, so you go up. Left and right motion of the left stick is your rudder. Move the stick to the right, the nose of the helicopter will go right. Left stick, nose left.

The right stick controls two things, called the "cyclic pitch", it is almost like the joystick of an airplane. Right motion will bank (tilt) the helicopter to the right, left left, back stick will raise the nose, forward stick will make the ground get closer in a hurry.

The helicopter wants to do things on its own too. The tail rotor is blowing to the right, so it pushes you to the left, so to stay in one place during hover you need to fly slightly right-skid low with the right stick a tiny bit to the right of center. The torque from the main motor/rotor wants to spin your nose to the left, so you need to vary the amount of left stick rudder motion to keep the nose straight as you climb and descend. Many helicopters have gyros to help with this part.

It's kind of complicated but you'll figure it out.

You really need at least 5 channels to fly any helicopter except for the most basic types. Most people use 6 channels so they can adjust their gyro in the air. If you have scale stuff like retracts you need even more channels.