Some are in fact words stems themselves. This is a very brief summary. A complete list of pronouns. Possesives take the adjectival form by adding the -a suffix. Any combination of the prefix and suffix will form a small word describing something.
Numbers follow a consistent pattern, best illustrated by example.
They are prepositions, conjunctions, interjections and even adverbs, and a real pain to always be looking up in a dictionary. Here is a fairly complete list of all you will likely meet. Compiled by Bernd Wechner, with much appreciated advice from Daniel Chung, Donald J. Harlow, David Wolff, Harri Laine, Martin R. Bartel, Jim Kingdon, and Bob Lidral.