Does all nodes have bundles? Also can we create custom bundles?
Bundles are an implementation of an entity type to which fields can be attached. You can consider bundles as subtypes of an entity. With content nodes, for example, you can generate subtypes like articles, blogs, or products. Not all entity types have bundles, however. For example, users do not have separate bundles or subtypes. With bundles, you can have as many subtypes as you want. Then, using the Field system, you can add additional fields to those bundles such as file download field for Articles and location fields for Users.