The PHB has what you are looking for on pg 15 Tiers of Play The shading in the Character Advancement table shows the four tiers of play. The tiers don’t have any rules associated with them; they are a general description of how the play experience changes as characters gain levels. In the first tier (levels 1-4), characters are effectively apprentice adventurers. They are learning the features that define them as members of particular classes, including the major choices that flavor their class features as they advance (such as a wizard’s Arcane Tradition or a fighter’s Martial Archetype). The threats they face are relatively minor, usually posing a danger to local farmsteads or villages. In the second tier (levels 5-10), characters come into their own. Many spellcasters gain access to 3rd-level spells at the start of this tier, crossing a new threshold of magical power with spells such as fireball and lightning bolt. At this tier, many weapon-using classes gain the ability to make multiple attacks in one round. These characters have become important, facing dangers that threaten cities and kingdoms. In the third tier (levels 11-16), characters have reached a level of power that sets them high above the ordinary populace and makes them special even among adventurers. At 11th level, many spellcasters gain access to 6th-level spells, some of which create effects previously impossible for player characters to achieve. Other characters gain features that allow them to make more attacks or do more impressive things with those attacks. These mighty adventurers often confront threats to whole regions and continents. At the fourth tier (levels 17-20), characters achieve the pinnacle of their class features, becoming heroic (or villainous) archetypes in their own right. The fate of the world or even the fundamental order of the multiverse might hang in the balance during their adventures.
