Q. where all on campus can i use my flex dollars? and can i use them at the little store in the cub building?

Flex is explained on the Student Accounts webpages.

While I do not find the answer to your specific question on these pages, my understanding is that Flex points can be used at the dining halls and any food service counters operated on campus by food services (Starbucks, the CUB, etc. -- but not for laundry or other coin-op machines).