This topic is so broad that it is necessary to divide it into several parts:
- Learn to use the rpm command,
- Learn to use the yum command,
- Learn to deal with package groups,
- Configure a remote repository,
- Configure a local repository,
- Manage repositories.
Don’t forget to check these yum guides. You can also download the Red Hat Yum command cheat sheet. Sander van Vugt provides an interesting video about installing and updating software packages (7min/2016). Additionally, you can watch Red Hat videos about Resolving Dependencies Issues (9min/2016) or How do I manage software in RHEL? (13min/2017).
Although not in the RHCSA and RHCE curriculums, you should become familiar with the deltarpms. At some point, you may want to prevent some packages from being updated. Also, you can read this mail to better understand rpmnew and rpmsave files. You can also read this article about the installation of Foreman on CentOS 6. Finally, if you plan to create new RPM packages (still not part of RHCSA/RHCE curriculums), you need to read the RPM Packaging Guide.