I found this sight for you, scroll down past all the links and it will give you detailed instructions on how do get this done. Good luck to you.http//www.immihelp.com/visas/visitor/sponsordocs.html
How Do I Write A Letter Of Invitation For A Friend To Enter The USA?
What is the nationality of the visiting friend? If British then no as they are eligible for the VWP aka Visa Waver Program.