There are some videos on the mfr. pages here: Mastercool Inc., Flaring ToolsJon:
That Masterkool tool that bill is describing is awesome. Uses well made sets of dies, with a straight-on hydraulic ram. It also has no problem double flaring stainless tubing.
I have this tool, and have enjoyed using it recently while making new 3/16" stainless brake lines on the SLC (I decided I wanted the front brake lines to run outside the car instead of inside).If your looking to do a really professional job, i think these expensive ones are the way to go. I have used those cheap ones with the split die, and they work, but they are a lot of trouble and only do a single flare. If i was building a car, i would definitely look at these expensive ones.
Professional Brake Tubing Flaring Tool - Brake Flaring Tool - Brake Tube Flaring
Flare Pro 4 in 1 Flaring and Swaging Tool