Sinterklaas is actually closely interwined with Christmas. When the Dutch "owned" New York, then called New Amsterdam they brought this feast with them. Sinterklaas(Saint Nicholas) was part(among lots of other things) of the basis of what is now Christmas. This holiday evolved and got an whole other look and story it than Sinterklaas and came back to the Netherlands as Christmas.
Sinterklaas is a traditional giftgiver in the Netherlands. He is the saint St. Nicholas(patron saint of among other things: Children.) Sinterklaas is celebrated on the 5th of december when Santa brings the nice kids gifts and his helper black Peter(probably originated from Italian chimneysweep festival) takes bad kids in his bag to Spain, where Sinterklaas and the Peters are from. Sinterklaas arrives in The Netherlands with a steam boat about two weeks before december 5th. The 'official' Sinterklaas comes to a different city or village each year(which can be followed on tv.) In the rest of the cities help Sinterklaases arrive in the harbor. The black Peters throws traditional Dutch Candy to the children. In those two weeks children set there shoe by the fire place and Sinterklaas fills it with little gifts. The children often leave drawings for Sinterklaas and the Peters or a carrot and hay for the horse. The 5th of december is called package-evening. Usually the family sits together, than there usually is a loud banging on the door and some candy is thrown through the mailbox. A box of gifts is left in front of the front door.
The official Sinterklaas
Grown ups also celebrate it. They often draw names to select one person they have to buy a gift for and than have to make a "suprise" with a poem to accompany the gift. This means the gifts will have a very creative (self made) packaging that has something to do with the receiver. For example my brother once made a soccerfield with little puppets on top if it, he hid gifts in the field and small ones in the carboard puppets. The poems are often funny and are often somewhat teasing.
The leader of the best show about Sinterklaas that was ever made(in my opinion.) After the leader it is all in Dutch/Flemish. It is a Belgian show because they also celebrate Sinterklaas there. There are more countries and areas where it is celebrated, but they all have other traditions and aspects of the holiday.