Volumes in Stingray are used for Navigation and tagging the NavMesh on generation. For more details, see "Tagging the NavMesh at generation time" in Generate navigation mesh. You can also use volumes for non-interactive interactions such as to detect entering certain areas in rooms etc.
Do either of the following:
In the Level Viewport, click to place the first volume point.
Click again to place another volume point. (Repeat to add additional volume points.)
Click on the first volume point to commit the base shape.
Drag up or down to set the height of the volume.
Click to commit.
Select a volume.
Select the Create > Volume from the main menu bar.
Points display on all corners of the volume shape.