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You will need to add your bank account or credit card into the coinbase system, be verified then you can deposit and withdraw.

Depends on your country of origin. Coinbase doesnt allow purchases in many countries. Its just used as awallet. You need to find an exchange in your own country that allows you to convert fiat to btc....then you can convert your btc to steem. Hope this helps :-)

Oh! Thanks alot. This much helpful.