Page list custom templates
Custom templates are unique view layers which can be made for any type of block in a concrete5 install. Underneath the fancy webpages, a custom template is a PHP file, each block type has a directory for them. When you are in edit mode for a page, you can choose to set a custom template for a block by selecting the block, and choosing "Custom Template". You will be presented with a list of available custom templates for this block type. Here is a great place to lean more about custom templates.