The RFD is a component of a supercell. Most simply I can put it is that the rotating updraft causes pressure perturbations in the vertical structure. A high in the middle of the storm and low pressure at the surface. This drives mid level air towards the ground, which is what we call the RFD.
Now all supercells do not produce tornadoes, therefore RFDs are not only present when tornadoes are present.
Some research does suggest the character of the RFD (i.e. warm, buoyant vs. cold, stable) can be a possible source of tornadogenesis. But there is other work that suggest that horizontal vorticity of the forward flank being ingested is a larger driver. Which is to say that we really don't fully understand tornadogenesis.
But Dr. Orf's simulations are pretty jaw dropping FYI.