There are many species of birds and many varieties of each species. It's a great thrill to spot a bird that is rare to an area or is not seen very often in any area. Many birders keep a list of the birds they identify. There are backyard lists, county lists, life lists etc. Competitions are sprouting up in many places.
Birders try to find more species than their competitors in a given amount of time.
Some people try to be the first to spot a species that is migrating across their area. The only equipment you really need in observing birds is your eyes. Yet, many birds can be identified by their sound alone. Guide books, about birds, can help you learn to identify birds. There are many bird guide books in bookstores and libraries.