NetBIOS over TCP/IP uses 3 ports:
The NetBIOS API uses names to identify network ressources. The nbtstat command can be used to examine and configure NetBIOS names on a Windows system.
NetBIOS over TCP/IP in itself is just a transport protocol. However, as it is the typical transport protocol for the SMB/CIFS protocol in Windows systems, it is often confused with the SMB/CIFS protocol, which does the real work on Windows systems.
For technical details about NetBIOS over TCP/IP, the reference documentation is the NBT chapter  of Christopher Hertel's book, Implementing CIFS.