All u have to do is have a copy of the game that has HW registered to your account and do the main story quests till they lead u to HW, takes awhile but you'll get there eventually if u just keep doing your main story quests.

If you bought just the base game, I think it's the a realm reborn starting edition then that one is just arr and not the other expansions such as HW, my advice for anyone who decided to get this game is get the complete edition which includes all the expansions from a realm reborn to shadow bringers.