In Diablo 3 for the PC, there is no magical “auto attack” button that you can click until mobs are dead, unlike some other games out there. You have to do more work than that in this game sir!
However, there is somewhat of an auto attack feature if you do it right.
When attacking, if you hold down the any of the attack buttons, your character will keep swinging until you let go. If it’s a special attack that requires energy of some kind, then they will keep doing that special attack until the energy is depleted, and even then they will continue to use regular attacks until more energy is gained to do the special attack again.
If you hold down the shift button while clicking, your character will stand still as well, so you can essentially hold shift and the attack button to keep attacking in the same spot until you let go.