Welcome to AppImage. A good starting point for most questions is our wiki at https://github.com/AppImage/AppImageKit/wiki.
If there is no AppImage of your favorite application available, please request it from the author(s) of the application, e.g., as a feature request in the issue tracker of the application. For example, if you would like to see an AppImage of Mozilla Firefox, then please leave a comment at https://bugzilla.mozilla.org/show_bug.cgi?id=1249971. The more people request an AppImage from the upstream authors, the more likely is that an AppImage will be provided.
If you are an application author and would like to make your application available as an AppImage, please start here: https://github.com/AppImage/AppImageKit/wiki/Creating-AppImages. Feel free to open a GitHub Issue in the AppImageKit project if you need support using the tools provided by AppImageKit.
I would like to have my AppImage included in the AppImageHub central directory of available AppImages
Please see the AppImageHub Readme.
If you would like to report issues with AppImageKit itself, or would like to contribute to its development, please see our list of issues and get in touch with us in #AppImage on irc.freenode.net. We welcome pull requests addressing any of the open issues and/or other bugfixes and/or feature additions. In the case of complex feature additions, it is best to contact us first, before you spend much time.