Once you've found an ad that matches what you're looking for, you can save it as a favorite so that you can find it easily.
To mark a product as a favorite simply tap the heart icon that can be found by entering the product details.
The list of favorite products can be found in the Favorites section in the navigation bar.
If you want to remove a favorite from the list, simply tap the heart-shaped icon and the product will disappear from the list.