RPM and Repository
$repoquery #is to query packages from the repository and get information about the packages
$rpm -q #for installed packages, RPM better than repoquery because RPM allow you to go deeper with your query
Note: for downloaded packages using yumdownloader need to use rpm -qp packagename
$rpm -qa # will query all and show all the packages in the rpm database, packages that have been installed
$rpm -qf /etc/filename # to find the file coming from which package (etc/filename means any file, this only example)
$rpm -ql packagename # to see the list of the files in the package
$rpm -qc packagename # to see the config file for the package
$rpm -qd packagename # to find the documentation for the package such as readme etc