White Harbor is a large harbor town south of Winterfell where the White Knife river opens into the sea. The castle and town has more contact with the southern part of the realm than any other place in the North, and so the Manderlys follow the seven-sided Faith and employ more knights than other houses of the region. White Harbor itself was built by King Jon Stark after driving off seaborne raiders from the east.
Lord Manderly is extremely fat, moreso than even his sons. His he has two sons: his heir, Ser Wylis, and Ser Wendel.
Information about House Manderly that reveals spoilers from the books.