Hi Burr,

Have you checked out the introductory tutorials here:
http://moi3d.com/1.0/docs/tutorials.htm ?

Those videos show the tools in action while building some simple shapes, that may help introduce you to some of the terms since you can then see what they are actually doing in a real modeling session.

Things like tangent and perpendicular snaps are there to help you accurately place things while you are drawing.

It is not unusual for people to want to have a 90 degree angle in part of their overall design. They don't want something just kind of close to 90 degrees, they want to be sure that it really is 90 degrees. That's what something like Perpendicular snap is good for.

So for example if you have a line:



And part of your design you want to create involves having a second line meeting at a 90 degree angle to the first one, you can use Perp snap to draw that:




Tangent is similar, but tangent means pointing in the same direction like a 0 degree difference rather than a 90 degree difference.

Do you have some particular terms that you need more information on?

- Michael