You can go to the "Exchange" drop down menu found on the left side of your dashboard. After clicking on the exchange it will show a drop down menu of all the altcoins available for buy or sell. Chose which coin you would like to purchase by clicking on the appropriate coin link. On the next page you will see the current price at the top of the page as well as buy/sell orders in the boxes below the graph. You can buy and sell one of two ways. The first is you can choose the price you would like to buy the coins at, once you press the buy button, your BTC will go into escrow until someone offers the coins at the price you would like to buy them at or you cancel your buy order, there is a wait time for this kind of purchase until they are offered at the price you would like to buy at. The second and quickest way to buy instantly would be to choose a "buy" order with the amount preset, once you press the buy button the coins will be automatically credited to your account.
Learn More At The BTCpop Blog: https://blog.btcpop.co/