Templates are used to make life easier. On a plugin page, you can easily switch from one template to another. And once created, the same template can be used in multiple places, without needing to do any other work.
There are a number of templates available by default and you can also create your own custom templates. You can duplicate a default template and use it as a starting point or you can begin from scratch.
A rain template is the background code rain effect that is used on all plugin pages.
The "Settings" page contains general plugin settings. Right now, there are a couple of settings available related to the uninstallation of the plugin but when new settings are added, they will be accessible here.
A regular license allows an item to be used in one project for either personal or commercial use by you or on behalf of a client. The item cannot be offered for resale either on its own or as part of a project. Distribution of source files is not permitted.
An extended license allows an item to be used in unlimited projects for either personal or commercial use. The item cannot be offered for resale "as-is". It is allowed to distribute/sublicense the source files as part of a larger project.