The classical model varies from the normal acoustic guitar in that it is fitted with nylon strings. The pickup will be a transducer fitted underneath the bridge. This will pick up the vibration and the resonance that the guitar produces when played and either feed it straight out to an amplifier or through a tone shaping electronics module fitted in the body of the guitar.
The guitar may of course played without an amplifier, giving you that extra sound if you want to play to a larger audience. Although not as popular as a normal acoustic, there is still a wide choice of models available and companies such as Takamine, Yamaha and Martin make some fine classical electro acoustic guitars.