You can buy any altcoin in these market conditions as every altcoin is so cheap and you cannot get this price after some time. If you buy now and hold for next 6 months then you are a winner.
You can sell your coins at any exchange where they are listed but you have to create an account on that exchange before sell. List of exchanges of each coin is available on coinmarketcap.
bought bitcoin as this is the best and number one currency of this market and people have full faith on it. It gives regular and excellent returns every year and it will happen in future also.