Once you know your Archetype, you will next need to select your Power Sets. Each Archetype supplies two lists of Power Sets, one Primary and one Secondary. You will choose one Power Set from each list. This will form the thematic and functional core of your character.
In City of Heroes, Power Sets are literally lists of Powers, with each Power becoming available for player selection at various level milestones. In CoHd20, it's better to think of a Power Set as a kind of subclass in the Dungeons & Dragons sense, where your Archetype would be your core class. While a CoHd20 Power Set will provide "set features" at various levels, much like a D&D class or subclass provides class features, it is not as simple as the City of Heroes approach. CoHd20 keeps the name "Power Set" instead of something like "Sub-Archetype" to keep things simple and more or less aligned with City of Heroes. Each CoHd20 Power Set is mapped to one from City of Heroes. The features in each CoHd20 set are designed to invoke the spirit and feel of their City of Heroes counterparts, but refactored to better fit a d20 tabletop game.