Certain types of cards have two phases to their use: an activation phase and an effect phase. These are known as effect cards and are generally equipment cards or magic/psionics powers. The key difference about these types of cards is that they have two sets of keywords, one set that applies to being activated and one set for when it is in effect.
The simplest example of an effect card is a hand-grenade. The activation phase is throwing the grenade at the target. For this part, the first set of keywords are used. These will include a Range keyword along with other suitable keywords for a thrown weapon.
Once thrown, the grenade is activated and will explode at some point in the future. This is the effect phase and the second set of keywords take over. These will include keywords that control when it explodes and how much damage it will do.
Activating an effect card is done by performing a standard action. In the case of a hand grenade, it is the same as throwing any other object.
Once activated, the behaviour of the card will vary wildly depending on the nature of its effect. Generally the card goes into the static pool and has to be played to take advantage of the effect. Playing an activated card is exactly like playing other cards and it can be done during initiative actions, resistance actions or any other type of action where it is appropriate and available. The card's behaviour once played is dependent on its effect keywords.