content/ folder in a project is where all your data lives (in JSON format). This is typically divided into multiple subfolders that define your types. Types are just a way to group content of a similar structure. Individual files inside a type are very flexible, in fact you can define any field schema you'd like and there are no required keys. Even though files may be grouped together as a type, they can actually have variability between them in terms of their field structure - just make sure you account for this in your corresponding
Anything that appears at the first level within the content folder is a type. This can include single files such as
404.json, which are also types, but only have a one-off data source. You can define your own single file types this way if you'd like.
There is an optional, specially named file that goes inside your individual type folders named
_blueprint.json. This defines the default field schema for that specific type. The keys of the blueprint correspond to field names used in the content files and the values tell the kind of field that is being used. TODO: Currently the blueprint doesn't do much and there is no list of standardized values, but in the future this will be fleshed out and it will aid in generating scaffolding and tying into the CMS (see this issue).