Drafts in a home can come from a lot of sources, but something a lot of people overlook is the door threshold, you know that plate that runs across the bottom of your exterior doorways. Giving it a little attention may help you stop the chill of winter.
On most newer homes the threshold is adjustable. The wood or metal plate has several screws in it, and by tightening or loosening those screws the threshold can be raised or lowered, so that it seals the bottom of the door tightly.
Older homes may have a rubber gasket that tucks into slots in a metal plate. That gasket can get compressed or torn over time and may need to be replaced.
In either case your home will be a lot more comfortable if you stop the winter wind at the door.