A laser is just a stream of light where all of the 'light' is traveling in the same direction. That's as layman as I can think to put it. IOW - the light doesn't spread out as it travels and is of a single wavelength meaning only one 'color'.
If it helps you can think of it in terms of an oly vinyl record player. On a record, pivots and hills move a needle up and down creating an alternating current that ultimately gets amplified and forces your speakers to move in exactly the same fashion. On a CD or DVD pits diffuse laser light so that it doesn't get reflected back and no current is passed on. The electronics read this as a digital zero. If it is reflected, a sensor turns that light into an electric current which the electronics read as a 1. If you had a stream of 100 1's in a row though, the electronics would just get a continuous current, so it has to have some way of knowing how many 1's there were in that stream. For this they put a clock which is precisely calibrated for the speed at which they expect 'bits' (1's and 0's) to be coming in. From there the Digital to Analog (D/A) converter takes over and creates an analog signal just like the one that would have come out of your record player. This all happens blindingly fast....
On a CD, the 'words' are written with 16 1's and zeros, and they are read at a rate of 44,100 words per second. Per channel!!! That's over a million 1's and 0's processed every second just for 2 channel music. Now imagine how many are processed on Blue Ray and HDDVD.
Hope that helps a little.
