Indeed, going from OpenMP to MPI is not an automatic process (certainly not as simple as adding "MPI pragmas" to your application and recompiling). One of themain ideas behind MPI is that you run the same application for each process in your MPI communication domain, but different chunks of the data are processes by each process (called domain decomposition). Then those processes transfer their partial computations via send/receive calls to all the other processes (since none of them share address space as compared to OpenMP threads). That communication is done via MPI routines, which are provided to you with the Intel tools (e.g. Intel MPI Library).
I grossly oversimplified a lot of the ideas behind MPI, so I would recommend you take a look at Argonne's An Introduction to MPI tutorial. It also has some nice references to a few books which will help you get started.
Good luck in your MPI endeavors! We're certainly all here to support you :)