Understanding Cryptocurrency

I have a couple of friends who are really into cryptocurrencies. They’ve been swapping crypto for a while, and some of them have made a lot of money! They’ve encouraged me to get into crypto, too, and I’m honestly pretty intrigued. But I’m also very wary of investing in anything that I don’t fully understand myself — and I have to admit that I don’t understand cryptocurrency at all!
I’ve heard of the big cryptocurrencies, of course: my friends trade ones like XRP, for instance. But I don’t understand how cryptocurrencies actually work, or what they’re used for, and that makes me nervous. My friends seem to be bad at explaining all of this, so I’m hoping the experts can help!