Celebrating birthdays on Facebook is a great way to show your friends you care about them. Facebook birthday celebrations are fun, inexpensive, and easy to do. Here's how:

What to Do What It Is How to Do It
Write on their Timelines. Formerly called the “Wall,” this public forum usually fills up with well-wishes on a person’s birthday. Go to a friend’s Timeline, find the Share box below their cover photo and enter your message.
Poke them. A poke is a casual gesture that can mean “I’m thinking of you.” Only the recipients are aware of your poke. Go to a friend’s Timeline and click the gear icon in the bottom right of her cover photo. Select Poke from the menu that appears.
Tag them in a status update. Status updates are your own posts to your friends on Facebook. You can add tags to posts to give a shout-out to the people you mention. Go to your Timeline and start typing a status in the Share box. Then begin typing your friend's name. Select your friend's name from the list that appears, and when you post, he'll be notified.
Give them a gift. Facebook’s gift shop allows you to purchase gifts for friends. Facebook handles the credit card transactions and getting your friends' addresses for shipping real gifts. Go to their Timelines and click the Give Gift button in the bottom right of their cover photo. A gift shop window opens where you can browse gifts both digital (like gift cards) and analog (like candy).
Call them. This is a good old-fashioned verbal birthday wish. Go to their Timelines, click the Info tab, and look for their phone number located under Contact Info. Use your phone to call them up!