The buffalo was a very important part of the plains indians lives. They used it for many different things including ceremonies.
Tipis
They used the buffalo hide to make the tipi. This kept them warm in the winter but also worked reversibly and kept them cool in the summer so it was fit for all purposes.
Buffalo dung
Used for fuel.
The bladder/intestines
This could be used as food bag, buckets and cooking vessels.
Sinews
Used as bow strings.
This was important as the indians were always hunting so this was an essential part of their lifestyle.