first you have to decide if you want to learn about bitcoin or if you want to learn about investing! these two topics are very different from each other.
as for learning about bitcoin itself, as in the technology, the Mastering Bitcoin book is excellent to learn the basics and have a better understanding of how the technology works at an intermediate level.

but for "investing in cryptocurrencies" subject i'm afraid there is no good books out there because investing in this market is not something that you can write a book about, specially if you are talking about investing in manipulated, pump and dump altcoins.

I often tell my friends about Bitcoin and other cryptocurrencies. Many of them are interested in the idea of cryptocurrency, but they are afraid to invest now.

In the first place I think you need the know what blockchain technology is? what are the features, and usages of it also?

I can suggest Mastering Bitcoin (2nd edition) as a great resource. I believe its available on github for free, but I would buy it to support the author.