These accounts are ways to pay for qualified healthcare expenses with pre-tax dollars, but they differ in several ways. Individuals can contribute to an HSA if enrolled in a qualifying HDPD. The individual owns these accounts, and the money does not expire.
An FSA is an account that individuals can contribute to in order to pay for qualifying expenses with pre-tax dollars; however, there are limits to rolling over the funds from year to year. FSAs should be primarily used for known and anticipated healthcare spending because of the 'use it or lose it' feature.