The card's powers are:
You may not play this card on a check against a bane that has a power that happens before you act.
For your combat check, shuffle this card into your deck to use your Dexterity or Ranged skill + 1d12. You may additionally bury this card to add another 1d12.
Discard this card to add 1d6 to a combat check by a character at another location.
The first sentence applies to any playing of the card -- whether for the combat check power or for the assistance power. From the image on the card (of a rifle set on a bipod), I think the thematic idea is it takes time to set up this gun for use.
The perhaps unclear aspect is "before you act". One might think it matters who is the "you". But it doesn't. Vic has said that before you act is about "when", not "who". (I'd link his post but I'm in a rush this morning.)