As you likely know, the Blueprints that are provided by Confluence provide you with an index page, which displays all the pages created with that Blueprint. You can achieve the same thing with a template that you have created; you just have to take a few more steps.
Create a page in the appropriate space and title it as desired.
Choose the Insert Macro dropdown and then select Other Macros.
Select Confluence Content and then the Content Report Table Macro.
In the appropriate boxes, put the label(s) of the pages you wish to be displayed (this is where you use the label from the template that we mentioned on the Template page) and the space you wish to pull those pages from.
Your index should then display the pages created with that label. If you have previously made pages that you wish to be displayed here (say you forgot to add a label to the template until now), all you have to do is return to those pages and add the label.