inspiredproduction

Hello, I am building a login site with multiple users. I understand how to build the login portion of the site, but I am stuck on a certain part. I am going to have several different organizations login this site and each organization needs to be able to see their page with their information on it. For instance, in the sign up portion of the code, I am going to have a drop down box that specifies their organization, for this purpose we'll call them organizations "A", "B", and "C". When a person from organization "A" registers and logins to their page, all of organization "A's" information needs to be displayed. Each individual needs to have their own page which belongs to a greater group called organization "A". Same goes for organizations "B" and "C". Also, there would be specified administrators for organizations "A", "B", and "C". How would I go about doing this? If anyone could point me in the right direction, I would really appreciate it.