OK this is a bit mysterious, but if you have some standard templates that you like to use, then Google has two completely different ways of doing this:
- If you have a personal account, then you create a dummy document with your styles and layouts loaded into it. Then when when you create a document, you click on themes for Google Slides and then choose import template at the bottom and select your slide deck.
- If you have an organizational account, then there is an actual template directory in https://google.com/drive/templates and you can stick it in there and it appears in the template gallery
