Q: why can't i get pages to use "auto-capitalization".  i tried preferences but i find not tab for this

Because you are using Pages 5.x?, the one with the 120+ missing features?

Peter

ibid. What Peter said.

Additionally, macOS Sierra now provides two additional settings to the correct spelling automatically on the System Preferences : Keyboard panel : Text panel:

and the descriptions for these two new features:

Pages v6 on macOS Sierra still has no provision for auto-capitalization when the above is checked.

As far as I can tell, Apple decided writers need collaboration, and document tabs in Pages v6 more than useful, practical features that have been missing for three years.

Pages v6 is restricted to macOS Sierra (10.12). You can see your version by the Pages application menu : About Pages.