Worst onboarding ever

I have only started two months ago, I have yet to be provided any proper onboarding (only now received a generic company onboarding), and my manager has immediately put me to work with little to no indications on what is expected from me, what I need to achieve to pass my probation and what to do with the tasks I’ve been assigned. I’m scared and frustrated. I was told that in order for my Manager to trust me, they need to know they can call me in the middle of the night and would pick up.

I’m a senior but never been in such situation before, the request to be ready to answer calls in the middle of night is something I’ve never heard before and I would never dare to request it from a junior resource