Basically I just recently got accepted to be an "it intern" for a commercial realty company in the area. There are 3 people within the team that I was hired as an intern for, and they wanted a central location where they would be able to find information or documents related to a certain job regardless of their current location. Any one of them would be able to upload files or enter information regarding a certain job and all three would be able to find that information quickly and easily at a later date.
The best idea that I could think of was to create a secure website that would, over time, be able to be run and updated by the three people within the team without having to wait for me to manually enter the information in. This is obviously a fairly complicated project for a person knowing only the basics of php/mysql (me

), however a great learning experience in my opinion as well.
So here I am starting out and I am wondering if the basic idea of this would be too complicated to even think about for a novice, or if it would be something very possible with the time, determination, and a little bit of help on the side.
To save some time and a couple of replies: if this is at all a possible project, the first questions I have regarding this would be:

What is an easy way to have a dynamic content section with php, so that the template stays the same, but the information changes? I have been browsing and browsing and the only thing I could find is a switch, case, default or similar setup. I have a feeling that there has got to be an easier way to do this than adding a case for each and every page for the website.

The next would deal with security. I know this can be a very complex field and should probably not be messed with by a newbie without risk of some serious holes. Are there any good scripts available that I would be able to use for free, or should I just go with finding a company to help me out with this?
Sorry for the long read, and any ideas/input would be greatly appreciated,
Reqless