Global Mapper v25.0

How do I calculate volume between two surfaces starting with two point-shapefiles?

I'm having troubles importing raster files I've made in Arcmap, I can't seem to figure out the correction sequence of steps to take.

I was given two point shapefiles that, in Arcmap, I know how to make TIN and Raster files from. However, I am at a loss of how to load these into Global Mapper. I can load the point files and make elevation grids, then combine those layers to get a difference grid, but the output for elevation just doesn't seem right (each layer's elevations are +\- 10 from about 1,515 ft.) and the output difference grid is giving me numbers around 4,500. 

Secondly, I'm not sure if im setting my boundaries correctly. I have a shapefile that is suppose to be my perimeter for the calculation, but don't know how to transcribe that into Global Mapper.

Sorry if these a little all-over-the-place. I couldn't find a good tutorial of how to do this, any help is greatly appreciated. Version 18.0