You will get it at level 25.
Here's a good spell list.
It's listed as experience, so you should get it automatically. I have a Level 20 Troubador alt, and I'm looking forward to getting that spell.
EDIT: FOrgot to add...
You will use it to get out of a sticky situation for yourself or group. Keep in mind that the group members must be within a certain distance to get the evac, else they will be left behind...yes, it has happened to me. :(
If it's obvious your group is about to get wiped from 5 red^^'s, good time to evac.
This is also good for certain legs of the J-Boots quest.
It's good to become familiar with where the Evac will take you in the zone, typically to the entrance, bell, or zone-in.
J-Boots quest Edited, Mon Jul 11 18:05:03 2005 by tutanbriarpaw