There are three different ways to level faster in World of Warcraft (WoW).
Through quests and open-world grinding:
In this case you complete your quests and fight monsters in the open world. This is not the fastest way, but the most varied.
With a dungeon group:
If you have a dungeon group, you can continuously complete dungeons up to the maximum level. This also provides the whole group with very good gear. The downside is that this can be very monotonous.
Through a level boost in WoW:
If you decide to get a wow lvl boost, you don't have to do anything. Your character will simply be boosted to the maximum level and you can play again.