You take on one or more roles as you play Paradox for each scene (a small segment of play that centers on some agenda in the fiction). When you do so, you then have clearly defined abilities and tasks in the game. These tasks and duties are defined by the specific role itself. All of these ideas lead into some of the central concepts of play, and they are defined as they are introduced here.
Taking on the role of the narrator means you become the manager of the fiction. You could say the world is the stage and you're the director, moving the props and actors as you wish. In this state you control everything except the Agents and Voices, painting the world in which they live. Your duty is to reach within yourself and describe this world and its inhabitants in detail, giving it life.
Last but not least, you need to keep the Agenda of the fiction in mind as you go. The Agenda is what needs addressed in the fiction which was agreed upon before the scene began. If you have agreed that the Agenda of the Scene is “Capture the local fugitive known as RAM”, then when you drive the fiction you need to keep that in mind. You have a wide latitude for interpreting the Agenda and it need not be resolved completely in the scene. Using the example of an Agenda, you could have a scene where one or more Agents meet with an informant at a coffee shop where ultimately they may learn important intelligence on RAM. This would lead towards the Agenda, without fully addressing it, and still be a valid scene.
You might have your Agent present in a scene. If so, you take on their stance in the fiction - Making their choices and pretending you are them. While the Narrator fleshes out the world around the Agent, you decide how they behave and act in response. You can just imagine you are an actor playing out the role of your Agent in the scene. It is your responsibility to address the Agenda in some fashion over the course of the Scene, just as the same is true for the Narrator.
When your Agent is present in the scene, they may have the Focus. If so, you can imagine there is a spotlight on them in the unfolding story. Having focus means your Agent is almost like the center of the Scene itself. The Focus is transferable, meaning you can surrender it to another player with the Agent role, or the Narrator. When your Agent holds the Focus of the game, they can use their Spotlight Features.
During scenes where you are neither Agent or Narrator, you take on the role of a Voice. This is just as it sounds, you take on the voice of a character not present in the scene. However even though they are not present, you imagine them as a viewer of the scene and they may narrate over it. In this role you get to add notes and even provide direction for the scene itself. You have control of the hidden, the details behind the action at hand. If Agents are confronting a violent thief in the night, you can explain what is going on in her head.
However you also have access to the role of Supervisor when you are playing a voice. This means you can send messages from the Agent's boss and communicate with them on the level of an authority. You can think of this as backseat driving the fiction, after a fashion.
These are all basic concepts you need to understand to play the game.
The Agenda is some part of the fiction upon which you and the other players agree needs to be addressed. It literally is the game plan of what is going on in the story at any moment. You use this as a cue when you make choices in play to shape the action.
Agendas may be very explicit or ambiguous, as long as everyone can agree that it is a valid one.