Hi,
Since you're new to the CMS I'd advise to have a look through the documentation for your specific Version and Development model instructions!
https://docs.kentico.com/k12
Here you should be able to find information about the structure and different features.
![Image Text](https://content.screencast.com/users/DavidTK/folders/Jing/media/0ef33f35-5c2b-4588-a694-5379dfa4f523/2018-12-14_1036.png)
In regards to your specific error, you say you have a template CMSTemplates.StrazCenter.EventSubpage
is this an actual page in the CMSTemplates folder or a page that uses this custom namespace?
If you're using the Portal Engine model you'll need to create templates in Kentico Admin interface and than Create a Page that uses that Template. If you have more details about your setup we might be able to be more specific.