Hi @MarkMaldaba,
We don't have installation instructions for CentOS 5.11, but I would just pick the instructions that seem the closest and try those as a starting point. We have instructions for RHEL 6.6 and RHEL 7.1+ on our documentation site.
The requirements should be in the installation instructions, for example it requires PostgreSQL 9.4+ or MySQL 5.6+. It also requires you to set up an Nginx server.
The URL is in the format of https://sitename.example.com/team_name, where site name is the name you choose for the service (for example, "mattermost") and team name is is the name of the team you create. You can have multiple teams, so the /team_name portion changes depending on the team.