Invoking PP3 is very straightforward. Since it is a command line program you only have to call it somehow and give a so-called input script as the parameter, see Input scripts. For example, entering
pp3 orion.pp3
on the command line starts PP3 and lets it generate the file
orion.pdf, which is a PDF file with a star map of
Orion. You can view this PDF with Acrobat Viewer, convert it
to a bitmap, or you can embed it into a text of yours.
Actually there are three possible output formats. By default, PP3 generates a LaTeX file in the current directory. But most people cannot do much with it, therefore certain commands in the input script trigger EPS or PDF output, see Output control.
PP3 can't generate bitmaps. If you need bitmaps you must use an appropriate program (e.g. GSView or the Gimp) for converting the vector data to bitmaps.