How do you feed your pet on World of Warcraft

Once you complete the hunter quest line to get whatever pet you want, right click on your pets details under your details at the top left. Select info. It will tell you which types of food your pet likes to eat. Get some of that type of food. usually you will have some in your inventory anyway. Now go into your spell-book and abilities. Go to the Beast Mastery tab on the right. Find "Feed Pet". Click on it. Now go into your inventory and find the food. Click on it. It will feed your pet.

A simple way to feed your pet is to create a macro to feed it. First, open up your macro interface by typing /macro into the chat edit box, this will bring up the interface. Select the character specific macro tab and hit the "new" button. Type in a name for the macro making sure the "?" icon is highlighted. Edit the macro as below:

#showtooltip Feed Pet
/cast feed pet
/use <item your pet likes>

This will cast feed pet and use the food that you put in (replace <item your pet likes> with the actual name of the food). Of course you will have to replace the item with another type of food if you switch pets and the new pet does not like the food, or if your pet out grows the food. There are some macros that will autoselect the food type based on the family of pet you currently have, but that is another question all together.