A classical guitar is a guitar that is used to play classical music. This guitar normally has 6 strings and they are made up of nylon. This guitar is not the acoustic guitar the acoustic has from 6 to 12 strings and they are made up of steel. They can commonly be mistaken because they are both made out of wood and don’t need a guitar amplifier. The classical guitar is played with your fingers you can either pluck it with your nails or fingertips. It's not used with a pick because there won’t be a difference since the strings aren’t made of steel and don't need a steadier strum.
This picture is of a Classical Guitar as you can see the classical guitar also has holes through the head where you tune the guitar.