The rules state pretty clearly when you can use cards , starting on page 11 of the rule book for action resolution , only the left side of the card is used when you draw cards for a result , you can use cards from your hand , inventory or journal during the cost step and/or the results step . card text is only active when it is in your hand/inventory or journal.
"The active player must perform the following action alone" Means that ONLY the active player can take the action , "Only the active player is forced to take the following action". means that all players who participated in the previous action COULD take part in this action but only the active player HAS to
