You need to make a surface between the edge of the outer bowl surface and the inner one. Then you will be able to join the three. How you make that surface the best way is not really possible to explain without you providing the file…
here is a video showing both methods, using Loft and PlanarSrf as @Helvetosaur says.
you should take a look at the Training manuals level 1 and 2 to learn how to model these things in Rhino. there are a lot of tutorials on the web but those books have a well made order from basic to complex.
I knew about the revolve command. The problem was that I had already created both surfaces and I needed to join them. Then Helvetosaur and Diego kindly explained to me that I should use either Loft or PlanarSrf to do that.
So I think that I am all set now. But I need to study in detail both of those commands.
Thanks again. The contribution that you and other experts make is tremendously helpful, and I appreciate it.