Creeping refers to the action of investigating the map and attacking an Creeps, usually with your own hero along with a few supporting units, to gain gold, hero products, and TBC Classic Gold experience. Even though your hero gains more expertise for fighting your competitors, killing creeps is a great way to build up them as you are still putting together a force.
As sources and anything that gives your hero a bonus are so essential in the first game, players who do not creep are at a huge disadvantage. There's the more conventional RTS base and army building, then there's the dungeon crawl/RPG facet of cheap WOW Classic Burning Crusade Gold combating and levelling your hero, and obtaining some additional resources to help with the base. Nailing this multitasking is just one of the game's most challenging aspects, but it is also why competitive Warcraft 3 is so exceptional.