In order to set up base configurations for Magento 2 Twitter Cards Module please go to Stores > Configuration > Magefan Extensions > Twitter Cards.
1. In order to enable an extension choose Yes in the Enable Extension select box.
2. Enter the Product Key which you will be able to find in your megafan account after purchasing the extension.
3. Set the Twitter User.
4. In the Default Twitter Image you can set Twitter Card image by default. The chosen image will be used for a page if it is not redefined, for example in product settings.
5. The Twitter Cards Description can be set by default in the Default Twitter Description.
Once you have finished don't forget to press the Save Config button.