Hello, in order to buy BTC through a crypto exchange, the user needs to register, verify his identity, link a digital wallet to his account, which is necessary for storing cryptocurrency, and a bank account. Reputable companies tend to release their own mobile applications so that customers can make transactions through smartphones at any time. I can recommend you to visit
https://crypocto.com/LTC_LTC-to-BTC_BTC to get acquainted with the information about the service that offers the most favorable conditions for exchanging cryptocurrency.