Help for veterans on excel

So lately I have been assisting one of our family friend who worked as a chartered accountant and expressed his wish to try his hands on Microsoft excel. He is now 80+ but still likes to practice accounts. Well, I was thinking if there is something out there, like the guide when adobe premiere pro is installed, you see which could help him learn the tool on his own( cant visit COVID around 😷. Any help or suggestion will be really appreciated. I have found most of my answers on this platform, and hence expecting for this too!!

Thanks and blessings from him in advance😇