The octave buttons are used to shift the keyboard up or down in one octave increments. This extends the range of the keyboard in either direction, which lets you play notes that lie outside the number of keys available.
The more buttons the device has, the more complex the input can be.
The transport controls are used to control playback, set the position of the playhead, start recording, activate the cycle region, or to move to the project start or end.
Faders can be either channel volume faders, pitch sliders, crossfaders or even EQs.
The pitch/modulation stick is used to change pitch or modulate a sound in real time with one single control.
More knobs (rotating controls) can give the user more dedicated control over the device – e.g., volume, effects, EQs, etc. Types of knobs may differ between endless type or step type.