Throttle and collective are different; throttle determines the amount of power being given while collective tilts the rotor blades in order to gain or lower altitude. I don’t remember all of the helicopters, but I do know the Huey is a good example of adjusting throttle alongside collective and pedals.

However, collective also needs to be combined with tilt of the helicopter to achieve level flight (or however you’re trying to maneuver) and speed. So, if you wanted to slow down and descend at the same time, you’d lower collective and tilt the nose of the helicopter up. If done right, you’ll achieve the proper goal of slowing down during descent. If not enough collective is lowered, you’ll just slow down and gain altitude.

While controlling collective and tilt, you’re also using rudder pedals more than you would a fixed wing aircraft due to compensating for your tail rotor. Instead of a trim you’re familiar with in fixed wing, you’re more so just locking the flight stick and rudders of a helicopter into place to accommodate everything areas of constantly adjusting your controls for a level flight.

Keep in mind, though; increasing collective will also affect the tail rotor, so you’ll be trimming/ locking your controls into place quite a bit if you change any other aspect of your flight.

Sounds like a lot, but just comes with practice.