LCD library

I kinda understand what the library is doing.

I don't think so....

The 'code' that you have shown is dealing with setting up the I/O pins of the Arduino, it does nothing to or for the LCD.

You might want to follow the LCD Initialization link at http://web.alfredstate.edu/weimandn. The information there outlines what has to be done to initialize the LCD module regardless of the processor or programming language that is used to accomplish that initialization.

Don