Dynamic Product ads use your store's visitor data to track your visitors' behavior and send them personalized ads based on the specific products they viewed.
For this reason, the text you choose to use in these ads need to potentially work next to all the different products your visitors may view.
Always check your ad preview clicking the button in the bottom right to understand where each text will be shown and see an example.
The Catalog Headline And Link Descriptions will also need to work with many different products or you can use dynamic text inputs to use the information in your Product catalog, like in the example below.
Click the plus signs and you will get the dynamic text input options.
If you would like to control the first image shown in the dynamic product carousel ad, you can create an intro card. More instructions on how to do that can be found here.