You have to onboard someone to Ethereum. 

What is your go-to to teach them what it’s all about?

Generally speaking, I don't onboard people to Ethereum. I onboard them to projects ON Ethereum. 

Blockchain is a tool like any other, I won't onboard people unless there's something in particular they could benefit from- usually nounish fundraising or the abundant creator support.

Professionally Nounish. Host @ The Noun Square, Nouncillor, Voice Actor, ENVtuber

Creator of NounCraft.gg

adding to this a bit:
The vast majority of people (in my circles anyway) simply don't care about provenance or self-custody or anything else blockchain tech enables. I think educating on the importance of those things WITHOUT the tech is the first real step. If they then care, they'll ask about eth themselves.