The server download page (en-us) says:

Should you want to start the server with it's graphical user interface you can leave out the "nogui" part.

"It's" there would expand to "it is", so "with it is graphical user interface". The word should be "its". Idiomatically, it may make sense to also replace "want" with "wish". The revised sentence would look like this:

Should you wish to start the server with its graphical user interface, you can leave out the "nogui" part.