Rosita Arvigo has lots of info/herbal suggestions/how tos for vaginal steams in her book "Rainforest Home Remedies: The Maya Way to Heal Your Body and Replenish Your Soul" I've loaned out my copy, so I don't have the exact info on hand.
From what I recall, though, you essentially put boiling water over herbs in a bowl. Sit in a chair that has the center part removed, cover lap/bottom of chair with a blanket. Think basically the same as a facial/nasal steam but for the yoni
Depending on the herbs used, it can help with everything from toning and tightening the vaginal tissues (as in after childbirth), helping with bartholin-type cysts, vaginal infections, hemorrhoidal tissue, or general external irritation to the yoni.
"Don't worry so much about 'Not Supposed To'. Hm? Live a little." - Armande Voizin in "Chocolat"