So, I'm obviously totally new at this modeling thing. I'm running through a bunch of tutorials with the hope to make some models I can print.

My question is this: How do I go about modeling surface detail like I'm seeing in the picture I am attaching? Most of this looks like I would just create geometry and extrude it a little to get the detail, but what about the circle in the middle?

How could I make the circular surface cutout and then build the bisected sphere shape in the middle of it? I tried looking into the Boolean options but the geometry I seem to get when I do that is not conducive to adding more detail.

I'm attaching a picture of what I got with the boolean attempt, I'm sure this is just a fundamental lack of polygon modeling knowledge on my part so I would appreciate any pointers.