forum software

Hi.
i do need to setup a system for my company to be easily accessed from the net.
i do need some kind of software to create a database and each of the workers to log in /register with their email.
then i need to create some kind of correlation between them somehow like facebook dot com does. For example three workers (A, B, C) register with the page and they are independent.
Worker A is friend with B
Worker B is friend with C
Worker A is NOT a friend with C and cannot see the files/attributes.

Any ideas on how to start?

I would start by looking through the available PHP CMS packages for something that has a decent rating amd suits your requirements.

http://php.opensourcecms.com/

This site hosts all the various projects so you can log in and try them look at the features, etc..
Some of the larger projeects like Joomla and Drupal have lots of plugins to add features and functionality..(Maybe a community plugin to add your user relations..dunno for sure) so don't overlook those..