How do I enable automatic updates of all packages?
There is no -main, -universe, -multiverse, or -restricted repository. Main, universe, etc are pockets within each repository. Packages from all pockets in an enabled repository are installed. There are only 4 repositories and they are all listed in that config file by default:
distro
distro-updates
distro-security
distro-proposed-updates
By default both updates and proposed-updates are commented out. Simply uncomment the -updates line if you want all updates instead of only security related ones.