Besides the usual degrees of comparison formed with -er and -more, there is also a double comparative degree with the...the...
Here are some examples:
The more you study, the more you know.
(The more you study, the more knowledge you have)
The younger you are, the happier you are.
(The younger you are, the happier you are)
Very often the more beautiful a girl is, the more foolish she is.
(Very often the more beautiful a girl is, the more foolish she is.)