Would love to learn by building a site which can host documents and contacts – where do I start?

Hi. Noob, so forgive my inadequacy here.

I have always been better at learning through building and doing. I was wondering if I can start from the very basic and work my way up, slowly slowly. I take pleasure in doing this much more than sitting through a lecture.

I was wondering where do I start if I have the goal of building an office “web-app” for my office team. We are 5 workers (mostly older) who need a web-based “application” through which we will be able to save the following:

• contacts (and all their info)
• user documents (mostly PDFs)
• share this database (meaining, we each have out own username and password, but the database itself is a single data source. So if we both go to a client named David, we both see the same files and information).

Any advice would be so appreciated!

Thanks so much and I wish you all a happy holiday!