How to play on the opposite side for opponents king? & Ideas in the sicilian

I have two questions —

1: What is usually the goal of playing on the opposite side from opponents king(usually queen-side).? I’ve heard that the goal is to create weak pawn & squares, and slowly win material or promote. So am I right or is there more to it?

2: So there is actually two questions about the Sicilian. The first one is what am I suppose to do when I play the Sicilian and my opponent castles king side? Because when they play the open and castle queen side, the plan is to attack the king if I’m not mistaken. But if the king is on the king side, does Sicilian just become a slow opening where black is slowly trying to create weaknesses on the queen side? The second question is if the Sicilian is meant for queen side play, why are there so many games where black attacks the king in the king side?