With Minwax, the stuff in the red can is a pre- stain sealer. On the can it says pre-stain conditioner (same thing). It goes on first, then whatever stain you want, then you finish with urethane.
The sealer ensures that you get an even color when you stain. If you don't use it, some woods can get a spotty look because different areas absorb stain differently. Cherry wood is an example of a wood that needs this before staining.
I use a ton of it on carvings because of all the exposed end grain, just like you'll get on a riser. Use it in a ventilated area though, it stinks and gives me a headache if I'm around it too long. The stuff works though, or I'd never use it.
Dave.