1. Visible in the list of community scripts with unrestricted access. Simply find the script by its name and add it to the chart.
2. Visible in the list of community scripts, but access is by invitation only. You'll need to find the script by its name and request access from its author.
3. Not visible in the list of community scripts, but accessible via a link. To add such a script to a chart, you need to have the link.
4. Not visible in the list of community scripts; access is by invitation only. You'll need both a link to the script and permission for access obtained from its author.