Circular polarization of light (or waves in general) corresponds to a spin angular momentum that arises as the polarization of the light is "spinning".
This "twist" is the wavefronts phase rotating or being staggered as it travels forward. Think of the wavefront of the twisted wave as looking like a piece of spiral pasta.
It is this spiraling that corresponds to orbital angular momentum.
Under what circumstance can you change the OAM in order to exert a torque? (or maybe vice-versa: What is an example of torque exerting a change in OAM on the wave?)
You can prepare waves in such a way that forces them into this spiraled waveform state. This can be done in a cavity (in the case of lasers) as there are solutions of the wave equation that give rise to OAM; or this can be done by using diffractive optics, like a hologram, that somewhat force the wave into this state. It is this case that you can think of a torque being exerted onto the waves.
Waves too, can exert torque on small particles (micron sized polystyrene spheres for instance). Light with spin or orbital angular momentum can be used to make these small object rotate!
