Congrats → well done :-))
1. Onboarding process
This depends a bit on the office but usually, you have 4-5 days of orientation either in your office, in another office, or off-site in one of McKinsey's facilities (e.g., Kitzbuehel).
In this week you learn mostly about logistics (e.g., how to use the tech, how to leverage the Firm's resources, how to deal with confidentiality), a few technical pieces of training (e.g., PowerPoint and Excel primers), plus a ton of networking with your intake. It's a fun week.
Staffing will then try to get you your first engagement, which could start right on the 2nd Monday. For some, it takes a bit longer and they are on the beach for 2-3 weeks.
You will get a very detailed roadmap about everything well in advance from your HR contact.
Benefits are non-negotiable at this level and also depend on the office. If you are in the DACH region, there is a car policy and allowance, for instance.
All the best in your new role!