For a fun and quick primer on feeding your backyard birds, check out this link
and scroll down to the video Bird Feeding in Winter.
In our imminent cold snap, there are things you can do to help your backyard birds. Some are noted in the video. You can also put a shallow pan of water (with some rocks artfully arranged!) in a sheltered place to give your feathered friends a drink. Make sure you check it frequently so it doesn't become a skating rink.
In the food department, try smearing small chunks of chilled bacon / meat grease on tree branches or fence rails. It's an easy way to give your backyard visitors an extra boost in cold weather.