Like with addons in the current game, you just need to drop any of these addons into the addons folder — find it under /Interface/AddOns/ in the Classic beta folder, which is in your World of Warcraft folder by default. Then once you log on to the game, you’ll want to make sure that the addons are enabled via the menu option on the character screen.
Discipline: Premonition - Heals nearby targets within 20 yards for [ 75% of Spell Power ], and applies Atonement to yourself. Deals [ PS * BC1 ] Shadow damage to yourself for each Atonement you have active, and increases their duration by [ 5 + 0.1% of Spell Power ] sec. Holy: Rapid Mending - Prayer of Mending is now instant cast, and its jump range is increased by 10 yards. Shadow: Void Origins - Void Eruption is now instant cast. Rogue