Amplitude: Amount of distortion
Periods: Amount of periods for this twirl

Twist
Twists a layer. "Whirlpool"-effect.

Amplitude: Amount of distortion

Lens
Distorts the current layer as if a lens was placed over it

Amplitude: Amount of distortion (lens strength)

Sinedistort
Distorts the current layer with a sineplasma

X Period: Periods fitting in the x-resolution
X Offset: Offset in the x-direction
X Turbulence: Amount of distortion in the x-direction
Y Period: Periods fitting in the y-resolution
Y Offset: Offset in the y-direction
Y Turbulence: Amount of distortion in the y-direction

Mapdistort
Distorts the current layer with a channel from another layer as a map
Useful with bump-maps

X Amplitude: Amount of distortion in the x-direction
Y Amplitude: Amount of distortion in the y-direction