Here is the official website but let me hit the highlights.
Make an account at the official website and you can download posters and checklists to make your counting easier. It is just fine if you cannot identify every single bird, just do your best to be accurate in what you do record.
Pick a few times you know you can watch outside, with or without binoculars. Have your checklist and a pen handy and go watch.
When you are finished, record your tally at the official website. Ta da! You will have collected data that scientists use to track birds. Some birds erupt - or just seem to appear in certain locations from year to year, while other seem to do short migrations depending on the weather.
The last few weeks, Shea and I have heard a Northern Flicker while waiting for the bus stop. After this heavy snow storm I doubt we will hear it again for weeks. Flickers like to eat bugs and finding bugs in all this snow will be impossible. But that mysterious hawk in the backyard, I am betting we will be seeing more of him since snow makes it easier to find mice and voles. Hopefully we will get a good look at him this weekend.
Photo from Snowy Owl, Jen Howard, ON, 2012 GBBC