RGB LED Light Strip - Arduino
Those LEDs need a controller to do anything, their default state is off.

You send them a serial data stream of 24 bits (8 bit Red, Green and Blue) per LED. The first LED in the chain takes the first 24 bits and uses them to set its color, it then outputs any further received data to its data output pin which is connected to the data input of the next LED. This way you can have a theoretically infinite length chain of LEDs, each set independently, driven from a single pin.

If the data line is idle for a 50us the data pass through mode resets and you are back to setting the first LED in the chain.

The timings required for reliable data transfer are fairly tight, on most micro controllers you generally you either need a library written in assembler or you can use an SPI bus interface and play some games with the data format to generate the correct timings on the output. There are libraries for the Arduino and other platforms that will handle the timing for you.

It would be possible to set them all to white and full brightness using a PWM output if you set the duty cycle and repeat period correctly. I have a 300 LED strip (with a little bit of coding they make good Christmas lights), all on full brightness pulls about 7.5 A so your power supply should be good for 48 of them.

The full data sheet is here: http://www.world-semi.com/details-106-4.html