You must use the services of a crypto exchange. Do not use the services of intermediaries if you do not want to lose money. There are a lot of scammers out there. I use the crypto exchange https://fast-change.net/ The work of this exchange suits me completely. The exchange rate is high, there are many different directions of exchange. Technical support solves all problems promptly. I changed btc to xmr. The exchange was made in 5 minutes
In fact, storing your coins in a cryptocurrency wallet is really important, but what if you have nothing to store? In that case you should buy crypto with credit card and j2tx.com can help you with that.
I used to buy cryptocurrency only on exchanges like Binance and OKEx, but there the whole process takes too much time, but on the above service I can buy cryptocurrency in just few minutes.