Welcome to Orchid, Kiryet!
Assuming your working with silver, the trick in soldering a
bezel cup to a ring shank is to get them to temperature at the
same time. Your shank is probably thicker and has much more mass
than the cup, so I would suggest keeping the flame on the shank-
the cup will get plenty hot from being in close proximity. The
other things to remember are to use enough flux and to make sure
both the solder and the parts to be joined are clean and free of
oxidization. A Bernzomatic should get hot enough to solder a
small piece like a ring with no problem.
HTH,
Lee