The module has 16 push buttons. You can make usual keypads for entering numbers, symbols, or navigate and selections in the program. There are pull-up resistors of different values for each button. This makes it possible to connect all the 16 keys to taking only one analogue port of the microcontroller. The button consists of two parts: a cap, which can be applied to any character, and a transparent cover which can prevent blurring of the text and add light.
After connecting power to the module and pressing at least one key contact at "OUT" will stress the appropriate level. Conformity stresses the buttons pressed, you can find out how on the board and in the table below (values are valid out when powered from 5v).
this video is about 4x3 keypad but the same concept: