Did you know you can earn Bitcoin on your PC very easily with Honeyminer?
Honeyminer uses your CPU and/or your GPU to collect Satoshi (which can be seen as a fraction of a Bitcoin, much like a penny is a fraction of a pound) in the background on your computer while you carry on with other things.
These Satoshi can then be transferred to a Bitcoin wallet where you keep all of your Bitcoins (there is a small fractional fee for the transfer).
For a good clean and simple example of a wallet take a look at HolyTransaction where you can store and exchange for other cryptocurrency or even real currency, although there may be a also small fee for conversion.
For more complex cryptocurrency trading you could use a platform such as Poloniex which has realtime multi-currency value tracking, trading between currencies and a multi-currency wallet to use.