When you create your Catalog, you will see some pre-made sets of products. Just like in Facebook, you will have the All Items default product set which contains all products from the catalog. In addition, to avoid promoting items which are not currently in stock, another default Product set will be available, with pre-determined all items that are in stock.

To create a Product set, go to the Product sets tab of your DPA Catalog, then click on the + Create Product Set!

New wizard will pop up, through which you can filter items you plan on using in your campaigns.

Here you can add as many conditions as you need.
The conditions function based on which field is selected and on the condition. The conditions work just like on Meta.
​
Additional thing you can do is choose between All Match or Any Match.

The first one means that all conditions need to be filled in order for an item to be in a product set, and the second one means that if any of the conditions are true for an item, that item will be in a product set.
​
After you save the product set, click save in the catalog page to request a sync for that, and after that you can use that Product set in any campaign or a template for that Catalog.