Ramit Seth

Hello! This is my first post in this forum, hope to have many fruitful conversations! ¡Estoy muy entsiasmado! I've been taught this phrase Pasarlo Bien and I know it means to have a good time, however my question is how to use it? How do I say, I had a good time, I'm having a good time and the likes? I search for it on google but all I could find was lo pasé bien or la pasé bien means I ha da good time, I'm not even sure whether it's la pasé bien or lo pasé bien. There's so much confusion for this on the internet. Someone help!