There are many Bitcoin, and Altcoin Exchanges. Knowing which to use and how to use them can be difficult to navigate. This is an area you either want to research or get good solid advice in. Exchanges come and go all the time.
The top 10 listed on coinmarketcap.com are Bitfinex, bitFlyer, HitBTC, Bithumb, Poloniex, Bitstamp, BTCC, GDAX, Binance, and Bittrex.(old needs to be updated) You can trade all kinds of Altcoins, Bitcoins, and other currencies at these exchanges.
Binance – A Large exchange that was located in Hong Kong but is planning a move. It is one of the easier to use exchanges.
YoBIT – Buy and sell on YoBit Exchange!
Bittrex – Another good exchange. It is easy to use and they just did a nice upgrade.
Midas – They started off as Shared Masternodes now they have many Investment opportunities plus an Exchange.