You may want to do a search for the method and you will find lots of details about how to do this.
Basically, you first put your hair in a ponytail, coat your ends with the product of your choice (many like to use vaseline) and cover the ends with a ziplock baggie.Secure the baggie over your ponytail with a scrunchie or stocking with the foot cut out. Then cover your baggie with a phony ponytail or make a bun.
I took my phony ponytail off and showed my baggie technique to my girlfriends lastnight. They laughed so hard about it but, they know it is the best thing for my ends.
I can't leave the baggie on for more then a day. I think it's because my hair is still short and after a while, my hair starts to feel heavy and sore from being up all day. I like to take it down at night to breathe.