These files are in PDF format. It is recommended that you read through the MPI Overview first. It is quite lengthy, so you might not want to print it out. Just use acroread. Not all pages will be of interest to you.
MPI Overview (PDF, 228K, 154 pages)
Compiling/Running Guide (PDF, 452K, 39 pages)
MPI Quick Reference Sheet (PDF, 69K, 15 pages)
Other documentation
(Argonne National Laboratory)