What is the button to attack on World of Warcraft

To start a basic auto attack, just right click on the mob/player you want to attack. This works a little differently depending on the class you play.

For melee and casters right clicking will start your basic auto attack. For melee this is good, not so much for casters.

For hunters, right clicking will either start your shooting auto attack or your melee auto attack, depending on the range from the target. If you are close to the target, you will melee auto attack, which is not so good for hunters, you need to get some distance on your target.

For all classes, your additional abilities and spells should be on your bars, and pushing those buttons should start the cast/ability you choose.