Rotate around selected vertices ? measurement box ? Freeze mesh?

How do I get blender to rotate around selected vertices. ?

I’m use to a measurement box that always tells me where n what size something is ,
Does blender have a box like this ?,a plug or something ?

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How does Blender freeze meshes so you can’t mess them up ?,while ya working on other meshes in the scene ?

Rotate what? The view? There’s a setting in User Preferences, Navigation, called “Orbit around selection”.

The “measurement box” exists in object mode. Open the side panel (N key), look for the Item tab, Transform. The same information can be found in Object Properties. In edit mode, the Transform box in side panel only shows median location or current selection.

Freeze? Well, you can disable object selectability. Or hide them. Or (in 2.79) put them on a layer and hide that. Or (in 2.8x) put them in a collection and disable it.

I googled n youtubed .Where is “disable object selectability” in 2.80 ?

There are two places to do that… in the outliner and in the object tab.