Weight lifting beginner??

hello! (sorry for the long ish post)

I'm looking for some advice on weight training because I am honestly so confused. I've been slim my whole life as I've always been on the swim team. I have completely kayla itsines's bbg guide and I want to start lifting weights to build more lean muscle and get more toned. My body fat percentage is around 14 %, however I don't feel like I look that lean and my goal is to have some more definition. I've never lifted before and I keep reading all these articles online with some saying lift moderate and high rep and other saying lift heavy and low rep??? Any advice on what to do? Thanks xx