What is confluence tool used for?

Confluence is documentation tool where you can store knowledge sharing articles, meeting notes, internal announcements etc. It is basically an internal Wikipedia.

Knowedge Base and collaboration. Basically you can use it like a internal team wiki

Documentation

For writing topics and sharing with others. Like google docs

The project involves documenting and tracking requirements.

In short, it is a tool to collaborate on content across an organization, track changes/workflows for policies and procedures, and even act as an internal communication (blog) tool. It is a great system for documentation, training, and new hire orientation. It can also be considered an internal website with individual spaces for your departments or areas, with the capability of enabling guest access for external audiences like vendors, etc.. Confluence is an Enterprise Content Management (ECM) system, or Content Management System (CMS) as many people think of and use it. It also has Document Management System (DMS) capabilities.