Analyze of the card:
It is an Artifact and placed in your Support Area. So, you can use it for all aspects of being an Artifact as long as you are the Felloship-Player (See Spot) e.g. for
Scroll of Isildur.
It is Unique. So you can only have one on the table (see Unique)
Skirmish: is a skirmish special ability. To use it you must take an action. Actions are done one by one. One you, one your opponent (see special ability, action, action procedure).
Since it has Skirmish: you can use the following gametext only during a skirmish.
This special Ability lacks of a limit, so you can use it as long as you can pay its cost. (see special ability, cost, limit, effect, spot)
http://lotrtcgwiki.com/wiki/_media/comprehensive.pdf