Coinbase does not host Steem. I use Coinbase is an exchange. I use it to turn my FIAT USD into Ethereum, then I got to Blocktrades.us to convert my Ether into Steem, Steem Power, or SBD.
In terms of exchanges Steem in on Bittrex, but I just prefer Blocktrades. Hope this helped.
Thanks so much for the reply. Yes, i get the part about having to buy BTC or ETH and then convert to steem, but I had heard there was something starting that had steem, front line, so the exchange didnt have to happen and was wondering if you knew about it. I think maybe a month old, tops. I will check out blocktrades. Thanks again!