The mechanics of running a Legion application will, of course, vary widely from one application to another. Generally, however, you will want to compile, register, and run individual applications with commands written specifically for that purpose. For example, MPI applications use the legion_mpi_register and legion_mpi_run commands, and PVM applications use the legion_pvm_register command. Some commands may require you to select a group of hosts that the application should use before running the application, others may just ask how many hosts should be used.
You can arrange parts of your context space around the needs of specific applications or to organize certain resources (a context for host objects that can be used for a specific MPI application, for instance).
Once you're ready to start an application, you can view its output with a tty object (a special Legion object that monitors and directs output from a shell's processes: see section A-2.0). The tty object can send your output to a file or a window.