You can add services like delivery, maintenance or advance payment in your product catalog. Services are added the same way as products.
To add a new service open All Products or Product Catalog page, and then click on the [Add new product] button.
The difference is when choosing a category. The key is to choose a category that has Track stock option set to No. This means that products added to this category aren't tracked on stock and are treated as services.
Click on [CREATE] button or press F9 keyboard key to save the changes, or click on the [CANCEL] button to ignore the changes.