How can I help my friend become a permanent resident?

There is no visa category for a U.S. citizen to petition for a friend to gain immigration benefits. Instead, your friend would need to assess potential eligibility based upon a family relationship or employment. The details and considerations about either a family-based or employment-based immigration case are far too detailed and complex to be addressed in a reply in this forum. If your friend has a family relationship or an employer or potential employer who may be willing to sponsor your friend, then it would be wise for your friend to schedule a consultation with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your friend's goals, and who then could offer legal representation in the often complex application process.