In my experience, there are three different types of flares:
1: Household gas line flare, used on flex hose connections between gas feed and dryer/furnace/stove etc.
2: Automotive flare, like in AN style fittings. Same principle as above (single flare), but the angle is different and the threads difference so they arent compatible. One is 37 degrees and the other 42 I think.
3: Brake and Cluch double flare. This is what you need to be using. On the above two, when you get done flaring the pipe, the pipe itself will have a concave flare, where as the fittings have the convex type. The opposite applies to the double flare. The pipe will have a convex flare, the bubble you might be talking about, and then the fittings have a machined out part inside of them to accept the flared end.
Id go to a repair shop or even a clutch and brake specialist place and ask them how to use the tool if you can't find instructions.
