What is a repository? What is the sources.list file?
Repositories are particular locations on the web which contain the thousands of packages (each containing programs, applications, etc) that you may need on your computer. The sources.list file contains the list of all the repositories that will be used to download packages in Synaptic and APT; it is located in /etc/apt/. Since /etc is the directory for system-wide configurations, you will require root privileges to edit it (root is your username and the password that you will need to have setup during installation process of Peach OSI).