I need to know some things about Foamboard guys

1)what is it?

2)can i get it at wal-mart?

3)is it paitible?

Also, what else to you use for dioramas? What is paster? Do you make it, or does it come as is? If you make it, please tell me how!

Anything else I should know before getting into the world of making dioramas?????