Most of us know what a Robin looks like. We probably fed Mallard Ducks at the pond. We could even identify a Bald Eagle or a Canada Goose without much effort. It helps to have a Field Guide for the birds of your area. If you know where to look in the book, you might be able to find a picture of your bird.
Computer programs are incredibly helpful for identifying birds.
To answer that question, you need a checklist of the birds of your area. Also includes State and Province bird checklists. Field Guides for the US and Canada Search the entire aisle for dozens of great books that will help you identify birds. Field Guides for the Rest of the World Search the entire aisle for dozens of great books that will help you identify birds of other countries.