How do I go about training a new hire?

I work as a Sr. Network Engineer for a hospital. We have 2 main hospitals and about 50 remote clinics totaling about 4000 users, 10000+ devices, 250 switches, 300 access points, 2 SAN’s, 4 firewalls, clearpass, solarwinds, etc. I have been solely in charge of the network including all switches, routers, wireless, vpns, firewalls and anything else network/storage/security/VM related, as well as all daily tickets, projects, and lights on work, for the past 16 years.

We finally got a new CEO who realizes this is kind of crazy and has approved hiring another network engineer. He is actually coming from a very similar environment (hospital) and has similar qualifications as me so I don’t need to worry about showing him the basics.

My question is, what’s the best way to go about training him on our environment and getting him up to speed so he can start to alleviate some of my workload? Just looking for some tips from others who have done this in the past, as I have not.