Recommendation letters (recs) are letters written by alumnae vouching for a PNM to their own sorority. Whether you need them depends almost entirely on your school, and this is the single most panicked-about topic that usually doesn't need panic.
Do you need them? At most campuses today: no, they're optional or not used at all, and every NPC organization officially states a PNM cannot be denied membership for lacking one. At some schools, particularly big Southern recruitment schools, they're still customary and having them helps you get seen. The answer is always on your school's Panhellenic page or one email away from their recruitment VP. Check that before doing anything else.
If your school uses them, here's the process. Each rec goes to a specific chapter and must be written by an alumna of that chapter. You don't send them, she does, usually through the organization's official online portal. So the task is finding alumnae: family friends, your mom's coworkers, teachers, your dentist, honestly anyone. Post in local alumnae Facebook groups or ask your local Panhellenic association, many keep lists of alumnae willing to write recs for PNMs they've never met (you'd send them your resume and photos and they handle the rest).
Timing: alumnae typically submit them in early-to-mid summer before fall recruitment. Ask by June, provide your resume and a couple of nice photos, and send a thank-you note after. Handwritten thank-yous to rec writers is one tradition worth keeping.
What if you can't get one for every chapter? Genuinely fine. Cover what you can, prioritize nothing, and let it go. Girls receive bids every year at every school with zero recs. The conversations during the week outweigh a letter from a stranger every single time.