In PersistenceMapping - how things are represented in a database - AutoGuid represents an dbgenerated Guid value.
As you state that you are new to MDriven you will probably not be interested in overriding persistence mapping just yet -> forget about AutoGuid for now.
Common types for attributes are the simple native types:
-String (size limited in db)
- Text (Text in db - no size limit)
- Blob (Binary data byte -combine with setting for BlobType) Guid