Ask Slashdot: What's the Best Linux Resource for a Retired Windows User?

Slashdot reader Leading Edge Boomer wants to help "a retired friend whose personal computing has always been with Windows."
But recently, they were gifted a laptop that's running "some version of Linux..."Probably he's not even aware that there are different distributions for different purposes. He seems open to learning about this different world. What recommendations might Slashdot readers have to bring him up to speed as a competent Linux user? I really don't want to hold his hand, and he's s