Is there a complete guide to how to use Apple Mail (in Mac OS 10.13.6)?

I'm just starting to use Apple Mail as my computer email program after years of Entourage and Earthlink Webmail. I haven't been able to figure out yet how to do a lot of important things and I'm afraid to delete emails on Entourage or the server. Can anyone point me to an Apple (or any) support article or PDF that covers everything--or at least the basics, like how to save emails to the Sent folder, how to indent and do bullets, how to enlarge text, etc. etc.? (Something with explanations would be nice, too. Like, what's a "VIP" mail and why should I care?) Thanks for any help out there!