Full Idea
The elimination rule for the universal quantifier concerns the use of a universal proposition as a premiss to establish some conclusion, whilst the introduction rule concerns what is required by way of a premiss for a universal proposition as conclusion.
Gist of Idea
Universal elimination if you start with the universal, introduction if you want to end with it
Source
E.J. Lemmon (Beginning Logic [1965], 3.2)
Book Reference
Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.104
A Reaction
So if you start with the universal, you need to eliminate it, and if you start without it you need to introduce it.