Recommended: MPI Tutorial Introduction

MPI (Message Passing Interface) is the grandfather of all parallel programming systems. It is a series of routines that you can call from FORTRAN or C++ programs, and was developed in the early 1990s. This tutorial is a slow and easy introduction to MPI.

Wes Kendall. MPI Tutorial Introduction. Available at http://mpitutorial.com/tutorials/mpi-introduction/.