A character's Initiative modifier indicates how likely they are to give their side an edge when a conflict begins.
If the leader succeeds, this means the heroes seized initiative for this conflict and the first participant to act during each round will be someone from the Player Characters' side; if they fail, it means they have lost the initiative for this conflict and the first participant to act during each round will be one of their foes.
See the next page for an explanation of rounds and turns.
The warrior monk Silida and the mage Ricard are exploring the ruins of an old waterway when they come across a bronze golem (page 330) barring their way!
The Game Master calls for an Initiative Group Check, and Ricard is happy to have Silida be the leader. She only rolls a 6, but Ricard's Check is a 12 (even taking into account the -2 penalty caused by the armor he is wearing). Silida's total is now 7, which is enough to reach the golem's initiative score!
The Player Characters have seized the initiative, which means the first turn of each round will belong to either Silida or Ricard.
Note that even if a new participant joins an ongoing conflict scene, they will simply adapt to the existing initiative.