Normally, if you upload a SCORM 1.2 zip file when creating a unit, it will be automatically imported.
However, there are cases that this will not happen, and the file will simply appear as available to download. Common reasons for this are:
The content is not a SCORM 1.2 version (but some other standard).
The file is not packaged according to the SCORM 1.2 specification (very common case: The zip file contains a folder with all the files, rather than the files directly, as imposed by the standard). You can fix your file following these instructions.
Review this guide to learn more about SCORM 2004.