With Online Store 2.0 and compatible themes, merchants can add sections directly to collection page templates.
By default, all collections will be assigned to the Default collection template. Create templates and assign them to collections to have distinct sections for different collection pages.
In order to add sections to this template, first confirm you are using a compatible version.
Compatible Theme Versions
Add a Section to the Default Template
In the theme editor (Customize), use the page selector to open Collections, then Default collection.
In the left sidebar, click (+) Add section.
Select one of the available sections. Use the search field to search by section name.