Buying mud for indoor use

Hi guys
I've never really wammed with mud/clay, and I was wondering what stuff people actually bought? There seems to be all sorts of different clay powder.
On a related note, how much of the stuff do you actually need to get, say, a bucket full? 
I've never really wammed with mud/clay, and I was wondering what stuff people actually bought? There seems to be all sorts of different clay powder.

