Note: Templates (Obsidian Core) and the Templater (community plugin) use different syntax that can’t be mixed and matched.
They should have different folders to store the templates (for your sanity), so create, e.g., Templates-core and Templater folders. Templates with the {{date}} syntax go in Templates-core; Templater templates with the <% syntax go in the Templater folder. Yes, the naming isn’t ideal and confusing at first 
Once you’ve made your Templates and Templater templates and set the folders accordingly in settings, you don’t need to interact with those folders again unless you want to adjust the templates. (I keep these folders in a “meta” area along with my folder for attachments and other Obsidian related stuff).
In a new note → run the Templates/Templater command → choose the template from the correct modal list → the template will be applied or with Templater it may prompt you for input depending on what you’ve written in the template.
Have a look at these two posts below: