Intimidate is a melee skill that acts like a short duration Fear spell when it actually works. There are lots of little nuances to how it works but basically you should only use it if the creature is snared or you have lots of room to chase it without getting adds.

The first 20 points or so of this skill are MURDEROUS. It just doesn't seem to want to skill up until you've already got some points in it. Just spend some GM training points to get a jump start on it if you have them available.

Intimidate requires you to pass 3 checks before it will ever do anything. First you must successfully Intimidate your target (meaning you succeeded in your melee skill). Once you pass that skill check you then attempt to KICK the creature (even if you don't have the ability to KICK otherwise). IF your kick lands, THEN the Fear spell is triggered. Which the mob has a chance to resist.

So, you must succeed in your Intimidate skill, then you must land the kick that is triggered, then if the kick lands it triggers the fear spell which may or may not land. All in all it's not a very useful ability but can help when soloing or in rare occasions when grouping.

Most groups don't want you to practice it unless it's already a kite group.

Yes, it is much the same like a monks Mend ability. I too dumped points in it, then used it in the overthere fear kiting mobs.