A template for creating an OL3 map is basically a page with a set of placeholders that will be replaced when the plugin creates the map.
To be available, a template must be saved in the ``templates``folder in the folder where you have installed the plugin (usually ``~/.qgis2/python/plugins/ol3).
Check the basic.html`ìn the ``templates folder file to see a valid template and how placeholders are used.