The CyanogenMod Archive is a repository to preserve older versions of CyanogenMod, due to the demise of that organization (and also because LineageOS, its successor, is rightfully concentrating their limited resources on the most recent versions of Android). Older devices cannot always be made to run newer Android releases, thus the preservation of older sources for developers to use for these devices.
Note that setup and building instructions are not provided, as it is assumed that you are a developer with at least a working knowledge of git, GitHub, and repo, and have built your own Android sources before. If you need help with any of these, resources such as XDA-Developer are available, and if all else fails, Google Is Your Friend(tm).