Bulbapedia:Templates
Reference page for template creation.
Testing templates
While making a new template or a new revision of an existing template, it is often better to put it in a user subpage (make an article at User:<yourname>/<pagename>) until it is ready and approved. If creating a test page in your userspace, mind the userspace policy.
To test your subpage template creation with actual use, you can post it at the Bulbapedia Sandbox, just by adding {{User:<yourname>/<pagename>|test parameters}} to the page. This will transclude your page as if it was a template, despite not being in the template namespace.
If a template was recently updated, but pages which use it do not update to reflect the change, the specific pages can be forced to update their transcluded pages by hard-refreshing the server. This can be done by clicking the UTC clock in the top of your screen.