It's a weird thing to me at least --- there's some double-clicking and so forth, and one has to click the "Add Tool" button first or something like that (and I think you have to use the window close button to get out of the dialog).
covers adding a tool... it
is explained clearly in this video beginning at the 2:00 point
Also note for V-bits that the angle which one enters is taper, not bit angle, so for a 60 degree endmill enter 30, for a 90, enter 45.
Image here shows a Carbide 3D #301:
(yeah, I get confused making screengrabs late at night on a Windows machine)