Not an application but a process: 1) Run it. See what it does. 2) Read it. Identify main function(s). 3) Trace it. Use a debugger w/ breakpoints for this.

Not an application but a process: 1) Run it. See what it does. 2) Read it. Identify main function(s). 3) Trace it. Use a debugger w/ breakpoints for this. See if you can follow how it runs. 4) Print it. Review interesting parts that you don't quite understand away form a computer.