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My first buy was within Steemit and it was a bit confusing. If you have bitcoins and can get the QR to show up, Blocktrades is ok. I trade coins all the time, so I use an exchange. Once I found out that my "Steem Address" was just sponge-bob (without the @) I was able to buy on Poloniex and just send the Steem to my username here. Powering up!

Poloniex? trading platform or a broker?

It's the trading platform. You have to go with one you are comfortable with. I don't recommend keeping much money on ANY exchange as so many have had problems as they get bigger. I was lucky that I got out of MtGox, Bitstamp and Bitfinex weeks before they attracted the attention of hackers.

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