How do you setup an MPI on the cluster's nodes
 

I am trying to build a cluster and on all article on the internet there is no detailed information on how to setup the nodes, Such as how to make them communicate with each other and the master. I also want to know weather if configuring the MPI on each individual node is necessary because I have read that during the installation of the cluster you should configure the NFS server to export the entire (I think thats how it's done) hard drive to the rest of the nodes and that the /etc/fstab file should be modified on each node to import the NFS export so that they can acces the server's harddrive while it is thinking that it's using it's own. But what needs to be configured on the nodes when it comes to the MPI, should it be left alone and the exporting of the directories via nfs automatically set everything up on each node provided that the NFS setting were setup correctly, or do they need to be configured individually to be told where the server is?

I also want to know what makes the cluster share it's system resources with the other computers on the network, what is the name of the type of software that does this? Is it the MPI interface or is it something elese?