Again, it depends on whether you are simply holding the cryptocurrencies or whether you want to actively trade your account.
You’ll be best suited to find a broker in one of the major regulated countries, so US and Canada, the UK and Europe, and East (Hong Kong, South Korea, Japan, Singapore) and South East Asia (Singapore).
Again, it depends on where you live, whether you’re willing to provide KYC (know-your-customer) information to the exchange, and whether you already have some funds stored digitally in a wallet or with an exchange.
Some exchanges only allow funding an account with existing crypto currency, like bitcoin. No fiat currencies allowed.
Where do you live?