Question

how is functional text useful in everyday life?

it provides entertainment.
it helps you research information.
it provides information to aid task performance.
it persuades the reader to think a certain way.

Answer 1

Well, functional means "having or serving a utilitarian purpose; capable of serving the purpose for which it was designed" according to http://dictionary.reference.com/browse/functional

Now, there are other definitions, but that one applies to the use in the phrase functional text.

If anyone ever gets back to this question, hopefully that will help.