Hierarchal Model:

Use this option if you are exporting a model that will contain a hierarchy. (such as a bone)

Hierarchal Animated Model:

Use this option when you are exporting a hierarchical model with an animation.
Note: When using this option, make sure to set the number of frames you want to export with your animation from the frames selection below.

Pure Animation:

Use this option to export just the data for an animation.

Renegade Terrain:

Use this option to export your geometry in a renegade terrain format.

Skeleton:

This exports the hierarchy tree without any geometry or animation data.

Simple Mesh:

Use this option to export a mesh (model) with no hierarchy, no bones, and no animation.

Settings:

These extra settings become available depending on which type of export you have selected.

Smooth Vertex Normals Across Meshes

Smooths the look of curved surfaces.

Optimize Collision Detection

Generates data that will improve the speed of collision detection. Turning this on is definitely a good thing for Renegade. Its not needed for the RTS titles.

Export Using Existing Skeleton:

You can use this option if you are exporting a hierarchial model, a hierarchial animated model or pure animation. It allows you to select a skeleton.

Browse

Lets you browse for an existing skeleton you wish to use.

Frames:

Use this to set from which frame to which frame you plan to export. Make sure to set these when exporting animation data.

Review Log:

This opens a window that contains the various information about what was being exported.  Just so you can review what you've done if so desired.