Being That I am also new, I may not be the best advice. But what I did was bought ethereum and litecoin which can be traded into steem via shapeshift.io Coinbase sells ethereum, litecoin, and bitcoin. Bittrex, openledger, and poloniex which has been having lots of issues it seems lately, all trade crypto.

From what I can tell you pretty much have to start with one of the major coins, and then trade from there.