I highly advise to check your local exchange in your country if they offer a buy and sell option for convenience. But like what most have mentioned, avoid exchanges that require KYC function as such offers abysmal rates on buying/selling cryptocurrencies.

Preferably, once you purchase your coins in a given exchange, avoid putting them and storing them in that exchange for a long period of time. There have been histories of exchanges getting scammed and most of the BTCs stored were stolen. I highly advise that you purchase a hard wallet for maximum security of your coins and to avoid the problem of getting scammed.