So you start WoW, you're on your character
then you start HB, let it load
Then you want to select what kind of botting you want to do, if you're doing questing, select Questing; gathering, Gatherbuddy2
Then in order to actually use the bot, HB will require a Profile, one you'd download on the forum, make sure you know what the profile is for and how old it is.
To load a profile, Press Load Profile, then select the profile you downloaded and whatnot.
That should be it.
Press Start, and then you'll be prompted to select a CC(combat class)
Select one, and the bot will proceed to initialize and begin.