If draft mode is selected one gets either a gif representing the last plot output if any, otherwise the text output is given. Sucessive gifs require RELOAD/REFRESH on some browsers.
If pdf mode is selected a pdf file with all text and graphics suitable for printing is returned.
If dxf mode is selected and there is a 3d plot, then a dxf file is returned. Here is the dxf help page which includes pointers to a downloadable java dxf viewer.
If vrml mode is selected and a plot named fig3d is defined then a (VRML) `dot wrl' file is returned. Most browsers need a plugin to view VRML files. (VRML=Virtual Reality Markup Language). Here is the VRML help page which is a guide and a link to installing VRML viewer on your machine.