You Daven for Me and I’ll Daven for You. They will send you a booklet of which Tehillim to say daily with a name to daven for. Thats basically it. You will daven for him/her and s/he will daven for you. May all our Tefillos be answered l’tovah!
(You will also get a copy of the song “The Letter” a.k.a. “Daven for Me” from Dovid Gabay)