A 3.5-month-old kitten is moving in. What do I need to consider?

Hello, A 15-week-old Siamese kitten is moving in with us on Wednesday. The breeder told me she's very shy, which is why she's the last one available for adoption. I've never had a cat before and I'm a little confused about the process and the first few days/weeks. Everyone says something different. How do you…