Firstly, navigate to the Apps page, then choose Quick Compare from apps list.

please enable the app by ticking to "Enable Apps" checkbox here.

On the collection page (or any product listing section) there are two types of Compare button will be added to each product:

1. Compare Icon: will be placed on top-left of product image

when customer clicked, a notification will be shown like this:

2. Input checkbox: placed on under each product