[Alan] has just posted an Ubuntu screencast that will take you through a crash course in the Ubuntu repositories. If you are new to Ubuntu this will give you a much better grasp on how software repositories are handled.
The different types of updates are discussed: Security updates fix bugs that cause a system vulnerability. Updates (generic) are for bug fixes that aren’t a security threat. Proposed updates are for testing before an update hits the ‘updates’ section. Finally, backports are updates from a newer version that have been ‘backported‘ so systems running older versions of Ubuntu can have the benefit of newer features and fixed bugs.
He also provides some tips on selecting package sources (main, universe, restricted, and multiverse), and choosing the fastest mirror to reduce download times. This screencast is just part one and we hope to see 3rd party repositories, personal package archives, and repository caching covered in future installments.