House Stark of Winterfell is one of oldest of the Great Houses of Westeros. They trace their line back to the First Men, and once ruled as Kings of the North.
Their sigil is a grey direwolf on a field of white, and their words are "Winter is Coming".
Eddard (Ned) Stark is the patriarch of the Starks of Winterfell. Husband to Catelyn Tully, and father of Robb, Sansa, and Arya Stark, and Jon Snow.
Eddard is named as Hand of the King by his lifelong friend King Robert Baratheon, but things go badly for him after Robert's suspicious death.
Robb Stark is the eldest son of Eddard Stark and Catelyn Tully and the heir to Winterfell and the North.
Upon his father's imprisonment for treason, Robb raises his banners and marches south to free his father, but Ned Stark is executed, and Robb is named King in the North by his followers.
Sansa Stark is the oldest daughter of Lord Eddard and Lady Catelyn Stark.
Sansa has romantic notions about life in the capital, and the trappings of royalty, but learns the hard way that it's not all dancing and pretty dresses.
Margaery Tyrell is the only daughter of Lord Mace Tyrell and Lady Alerie Tyrell of the Reach. She is close to her brother, Ser Loras Tyrell, the Knight of Flowers. She is said to be as beautiful as she is clever.
Arya Stark is the younger daughter of Lord Eddard and Lady Catelyn Stark.
Unlike her older sister, Sansa, she has little interest in dresses and dancing, and would much rather learn to use a sword. She is very close to her half-brother Jon Snow.
Jon Snow is the base-born son of Eddard Stark. He was raised at Winterfell, and treated like any of the other children by his father. However, Catelyn Stark resented him as he was a constant reminder of her husband's infidelity.
As he nears adulthood, Jon makes the decision to join the Night's Watch where the circumstances of his birth would not matter.