I recently heard for the first time, but I haven't heard from any of my friends, and I would like to understand and maybe even study the topic.

There is no difference, as bitcoin is one type of cryptocurrency, by far the most popular and most expensive. There are about 1,000 cryptocurrencies on the market today. That's all I know, can anyone else throw in some other generally accepted fact here?

The total number of all existing cryptocurrencies is very difficult to say for sure, because new ones appear all the time and some already existing ones are not popular and actually cease to exist. To be on trend and to understand this whole topic, I have been using best cryptocurrency payment gateway for several years and all my friends too, otherwise I would know only about bitcoin and that's it, but at the moment among most known ones besides bitcoin, which appeared in the beginning of 2009, Ethereum, Ripple, Litecoin, Dash and Monero.