People poke their friends or friends of friends on Facebook for a lot of reasons (ex: just saying hello, getting their attention). When you poke someone, they'll receive a notification.
To poke someone:
- Go to your friend's Timeline
- Click on their cover photo
- Select Poke
When you poke someone, they'll see the poke icon along with your name on the right side of their News Feed or their pokes page when they're logged into Facebook on a computer. They may also receive a notification.
Keep in mind only the person you poke can see that you've poked them. If you don't want people poking you, you can block them.
Once you remove a poke from your homepage you can't get it back, but you're able to poke your friend again. Keep in mind you can't be poked by the same person unless you remove their poke first.