I’m going to start with “How To Win Friends and Influence People”
I remember reading Larry King’s “How to talk to anyone about anything” some years back and getting a good bit out of that one.
In fact, there are still bookstores where you can skim books. I find the smaller selection there easier to deal with than the infinity of choices at online stores.
Explaining concepts and ideas, in my opinion, is a bit different, so look at this article to get some ideas.[0]
The other side of this coin is the idea of "presentation", on which many books have been written. While they won't help you with personal communication specifically, they should cover getting your point across effectively, hopefully simply.
There's a well-known 10/20/30 rule of presentations by Guy Kawasaki, an early Apple employee [1], and of course, complex books, and entire courses. Skim.
Hopefully, others here can recommend what helped them.
[0] https://slidemodel.com/how-to-present-complex-concepts/
[1] https://slidemodel.com/the-10-20-30-rule-of-presentations/