Everything is very simple. You need to register on a reliable exchange and buy it there. I can recommend the Binance exchange to you. Here is the information, is Binance safe https://tradersunion.com/interesting-articles/is-binance-safe-key-facts-you-should-know/ . I recommend this particular exchange, because I myself have been working with it for about 2 years and everything is fine. There are a large number of different cryptocurrencies, not only xrp.