Arapaho is a member of a group of languages called the Algonquian languages. It is related to Blackfeet, Cheyenne, Gros Ventre, and many languages spoken in the northeastern US and Canada: Cree, Ojibwa, Micmac, Shawnee, Kickapoo and others. Many of the English words borrowed from Indian languages come from these Algonquian languages - canoe, wigwam, moose, wampum, moccasin, etc.

hello (m-f, f-f)
hello (m-m)
how are things?
things are good
what's happening?
nothing much
what's your name?
... that's my name
I don't know/understand
I know/understand
repeat it!
thank you

You should begin by memorizing the following. These expressions allow for basic conversational greetings, and also include words that will allow students to say in Arapaho that they don't understand things in class, need things repeated, and so forth.