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!
Here you should be able to find information about the structure and different features.
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.