You should first sit down with a pencil and paper and write out exactly what you want, and how you want it. That way, you can come back and say here's a plan I have, would you go about it this way?
Here are my thoughts:
I would start off by setting up exactly how I want my site to work. When a user comes to the site, what will they see? Or what will be the end result displayed at the company?
Now that I know what will be displayed, how will I got about storing it? If I use a database, what might the schema look like. [I'd draw something similar to my above post].
I've got the end result, and the databases laid out. Now what about the front-end for user input? How about those forms? What information will I put on them? Can it be changed by a general user, or a specific one?
I'd finally ask myself about administration. Will there be an administration area, or will this be a wiki type of implementation where each person is able to add / contribute and update it as needed. Will I need user-access controls or a user management system?
Once I get all my ideas down on paper, it's then a matter of just sitting down and knocking out each block, one at a time. It's like whittling a piece of wood. You don't just start hacking away. You plan, you see the shape, and then you take little steps to get to the end result. You need to do much of the same here. You need to plan what it's going to be, then take some small steps in coding to make it to the big end result.
All in all, I see a few files right off the bat:
1.) Database file to hold the connection to and info about the database
2.) Display functions to hold the functions necessary for display inside the company
3.) User Input files to hold the different input scenarios (editing, updating, creating)
4.) User account management holding functions for creating, editing, updating, and deleting users
5.) Permissions functions to check whether the user has permission to perform that action
The list could go on and on, but that's just a start. And it's really very basic. Some of them could even be split up into smaller files so as to decrease load times.