You can buy Ethereum from anywhere in the world if you have an internet connection, not just in the country where Ethereum is accepted or legalized. However, in a country where there is no legitimacy, it is a crime in the eyes of the law. To buy Ethereum, you first need to select an exchange, open an account there and do KYC as per the demand. Then buy Ethereum with it by depositing dollars or any other currency, later you can transfer it to your wallet.