You need an API key from the provider you chose in the component’s settings. So if you choose “Giphy” in the API provider setting, you need to add the API key you got from Giphy to the Giphy API key field. If you choose Tenor, you need to add the API key from Tenor to the Tenor API key field.
The topic about the component explains how to get the API keys: Discourse Gifs
If I remember correctly, you can no longer use Giphy for free.