How to fix leaky outdoor faucet
I would replace the entire sillcock (also called a stopcock, outdoor faucet, hose faucet, or spigot), because it looks like you lost the handle, too; in which case you  should watch this video: https://www.youtube.com/watch?v=Lj_nTbIWzfI, 

Or if you really intend to repair it, try this instead: https://www.youtube.com/watch?v=cALQ3PR7k30

Edit- One important tip that I should add about installing or replacing the sillcock- it should lean downward as it exits the building. The reason that sillcocks are long is so that the important parts (the actual valve with rubber gaskets or rings) can be protected from freezing (by being inside the building). And it needs to lean downward so that it can drain or else it will have water inside the valve body that can freeze.

Edit2- In response to your comment, there is no "type" in the way that you are thinking of this. I prefer to call it a sillcock. It may have a long valve/valve body, or a short one. Unless you see the manufacturers brand name on it, nobody could guess, and it makes no difference. 

The only way to know what you need is to take it apart. The bad gasket or rings should be obvious. Perhaps you can find replacement parts at a hardware store (or online). See the picture showing how to take this apart; be sure to turn off the (main) water before you take the sillcock apart. You may also need to use the sillcock key to unscrew the valve assembly. Once you have the valve assembly out, take it with you to the hardware store so that you purchase the correct size gasket(s) or whatever you need.