A:
You will need some sort of receiver or amplifier to power these and one that accepts the right input you need.
You could always spend around 200 for a basic AV receiver to hook them up with HDMI pass-through to your computer, or get a small basic T-amp for your iphone for less than $100.
The beauty of Klipsch, is that they are super efficient which means you don't need a lot of watts to play them loudly without distortion. A 40-80 Watt amp will be more than enough to blow your eardrums out ;)