All Helm charts are kept in the charts directory. To add a new chart, create a new subfolder with the name of your chart and then use Helm's expected file structure.
Use pull requests for any changes to main. You do not need to modify the gh-pages branch directly; any changes within charts will be pushed via Helm's Chart Releaser action. Note that those changes may be force-pushed, so be careful if adding branch protections to gh-pages.