Here is the help screen containing complete description and examples
Usage: RunAs <user> <password> [/V] [/B] [/I] <program name> [parameters]
Command line parameters:
User - Username in form DOMAIN\USER (for local accounts use .\USER format)
Password - Password for the user account
/V - Optional parameter. If specified, RunAs binds the process to the interactive user Desktop. (Use this parameter when starting interactive programs from services)
/B - Optional parameter. If specified, RunAs prints only minimal diagnostic information to the screen in case of errors.
/I - Optional parameter. If specified, RunAs makes the launched process inherit I/O handles of the RunAs console. Use this to redirect any input/outpup from/to external processes.
program name - Full name of the program file to launch. If the name includes spaces, enclose the entire name in double quotes.
parameters - Optional command line parameters that you want to pass to the program