I'm having difficulty in creating a surface from 3 points. This surface "covers" a corner made from 3 surfaces. I've attached a picture to show what I am explaining. Surface B is a vertical surface and Surface A is a horizontal surface. Surface C makes contact with and tangential to Surface B and Surface A at points 2 and 3 respectively. L1,2 lies on B and L1,3 lies on A. The resulting surface should be tangent to Surface A. It looks like what I need is a loft but I can't do a loft from a point to a line. Would anyone have any suggestions to getting this?
Create a Plane using those three points. Then use one of many different methods to create the surface you want - the simplest being to sketch three lines between the points, on the plane you just created, and then create a Planar Surface using them.
Oops, I didn't see that the grey area wasn't a straight line.
Create a sketch on the grey surface and then use a Splitline to give you an edge to use / a surface to be tangent to. That should get you most of the way there. I think boundary surface, maybe fill surface (it might force you to have all contacts tangent, i can't rmeember off the top of my head), will be what you end up using.