requests as input from the user two positive integers s and e, such that s < e.
outputs (i) the integer n belonging to [s,e] that generates the longest Hailstone sequence Sn, and (ii) the length of this longest Sn
i have no idea about how to use functions to implement this task...
Presumably you would implement a function to compute the "hailstone sequence" (whatever that is) for a given value, and then return the length of the sequence. You would then simply call this function multiple times in a loop from s to e and record the largest result.
EDIT: Wikipedia contains pseudocode for the hailstone function.