Difficult one... but bitcoin magazine is helpful, learnmeabitcoin.com had an easy explanation and an advanced one. Thebitcoinmanual.com or europeanbitcoiners or bitcoin-only.com are also nice ones. Also endthefud.org is a nice collection of articles.
2 nice visualizing sites: he doesnt have to read it, you need to bring an extra display and show it on that, so you can point stuff out. It can help alot.
mempool.space
bits.monospace.live