Look, its okay. That link i pasted you guides you through it all.
Simply start reading and following what it says from here onwards:
"Open up the roundcubemail folder and navigate to the config folder. In here you will find two files, db.inc.php.dist and main.inc.php.dist. Rename both of them to remove .dist. You now have db.inc.php and main.inc.php."
You edit these 2 files including the server names and passwords etc.
You'll work it out. We all have to start somewhere.
I guess youre allready moving on it, from what i see in the other thread.
Good step and good luck.