eBird was created as a way for birders to submit their bird sightings via the internet. It works in a very simple way: you sign-in, select a location and a few other facts about your outing, and then check off the birds you saw. You can also put in the number of birds you observed, but it isn’t required.
The important thing about eBird is that over time and with many users, a large amount of data is collected and can be browsed and researched. But it only is effective if you submit your sightings.
eBirding isn’t a perfect science but it is a perfect example of Citizen Science and the Long Tail of Birding. It’s hard to get into the habit of entering your sightings, but even if you enter a few checklists a month, it helps.