As of 2024, to obtain TeX Live on DVD, you can submit a request for a volunteer to burn and mail a DVD to you. TUG facilitates this process with the request form and mailing lists, but no longer provides DVDs itself, as explained on that page.
After mounting the DVD on your computer, follow the installation instructions or read the documentation.
If you want to update packages from CTAN after installation (this is not required, or even necessarily recommended), see these examples of using tlmgr.
Sources: the DVD includes the complete sources in the texlive/source directory, corresponding to Master/source in the repository.
Information about downloading the ISO image and burning your own DVD is available separately, as well as other ways to acquire TeX Live.