There are a couple of different approaches to playing Go Action Fun Time
The Traditional RPG
In which the XP sits behind a cardboard Screen of Omnipotence, and has the responsibility for creating and tracking everyone and everything that is not a Regular Cast Member. The XP does not play a RCM, but instead plays literally every Guest star and extra in the episode. The other players contribute what their individual characters (the RCM's) do. This has worked fine in countless systems and scenarios since the 1970's. Under this system, the XP has 10x the workload of the other players, and should never have to contribute towards pizza or soda (this has also been a rule since the 1970's).
These rules, and more particularly, any Episode supplements are written with this approach in mind, but there are other, looser approaches.
EXAMPLE:
(For clarity, the scenario is set in modern times)
XP: (To the players) "You enter the bar you have been directed to. It is dark and dingy, not quite a dive bar. A couple of TV's over the bar show sports events, and 1980's hair metal plays a little too loudly from the ceiling. There are a handful of patrons, seemingly locals, and ..." (rolls) "A few that might be prostitutes."
Player 1: "Is there a bouncer?"
XP: "No. But the barkeep is rather tall and burly - as are some of the waitresses."
PLAYER 2: "We approach the bar."
PLAYER 3: "Who's we?"
PLAYER 2: "Well, my character approaches the bar."
PLAYER 4: "We should all go."
PLAYER 3: "Fine. We all go to the bar."
XP: "You go to the bar. Right?" (PLAYER 1 nods.) "Before you can get the bartender's attention, and man in a silk suit approaches you and says, "Ah! The heroes I have been waiting for. I am to give you your next challenge...""
Story-telling RPG
In which only the barest outline of the Episode is worked out in advance, and the balance is made up as the game goes on. There might still be a designated XP who plays the extra's and Guest stars, but primarily plays the villain. The other players would be expected to fill in the gaps more often than the approach above.
EXAMPLE:
XP: (To the players) "You enter the bar you have been directed to. It is dark and dingy, not quite a dive bar. A couple of TV's over the bar show sports events, and 1980's hair metal plays a little too loudly from the ceiling. There are a handful of patrons." (to Player 1) "Describe one."
PLAYER 1: Is there a bouncer?"
XP: "Is there?"
PLAYER 1: "No."
PLAYER 2: "You can tell because we just walked right into the place."
PLAYER 4: "Not because he's not needed, but because the bar can't afford one."
XP: "Fine. So who is here?"
PLAYER 1: "A prostitute whose intentions are as obvious as her weight problem."
PLAYER 2: (When the XP points) "An old man in a wheel-chair wearing his army jacket from the last war. Wait - not that old - just well-worn."
PLAYER 3: "Three construction workers in those bright, hi-vis shirts they all have to wear now."
PLAYER 4: "They're joking about hiring the prostitute, but in an hour they'll quietly go home to their wives."
XP: "And..." (Pointing to Player 4)
PLAYER 4: "A young couple from uptown who are visibly horrified at the sort of establishment they stumbled into, but are determined to see this through for at least one drink."
XP: "Good. Now what?"
PLAYER 2: "We go to the bar."
PLAYER 3: "Who's we?"
PLAYER 2: "Well, my character approaches the bar."
PLAYER 4: "We should all go."
PLAYER 3: "Fine. We all go to the bar."
XP: "Someone describe the bartender."
PLAYER 1: "You know that nice sweet grandma that told you stories and baked you cookies? Well in this universe, she's a bartender."
XP: "Ooookay. BUT - before you can attract Granny's attention, a man in a silk suit approaches you and says, "Ah! The heroes I have been waiting for. I am to give you your next challenge..."