Cooking with a pizza stone
The stone requires no seasoning.

To prevent pizza from sticking to it you should dust it liberally with cornmeal before slapping a pizza on it. 

A pizza stone will not work well with a frozen pizza. The stone surface will simply be too blazing hot for it. You'll likely burn the bottom while still having a frozen top. There should be little issue with a refrigerated pizza, although I have not tried. However, you will want to be sure to let the pizza reach room temperature before cooking.

Update

Regarding cornmeal. I just realized that you're in the UK, and I'm not sure if you guys have a different term for it than the US. I'm referring to this cornmeal. You should also use the coarsest possible.