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Every node can only have one primary node type. The primary node type defines names, types and other characteristics of the properties, and the number of its allowed child nodes. Every node has a special property called jcr:primaryType that records the name of its primary node type. A node may also have one or more mixin types. These are node type definitions that can mandate extra characteristics (for example, more child nodes, properties and their respective names and types).
Data are stored in properties, which may hold simple values, such as numbers, strings or binary data of arbitrary length.
The JCR API provides methods to define node types and node properties, create or delete nodes, and add or delete properties from an existing node.
You can refer to the "6.2.3 Node Read Methods" in the JCR Specification document.