The Extra Episode appears in the PS3 version after clearing Produce Mode for the first time.
You can choose one girl out of Ryuugu Komachi's four girls (yes, Ritsuko is an option) and produce the group.
Put simply, it is a mode where you do the equivalent of work and Festivals in the main game. It is a given that the idols will be taking lessons independently, so as weeks progress, their status will automatically increase.
As with the main game, depending on your selected answers, the Memory Level increases will differ.
Finally, raising them to Memory Level 5 requires the correct answers for every section, and will result in a perfect clear.
Because their status is increased automatically, you will not be put in a situation where it is impossible to win. Even if you do lose, there is the option to retry and this has no effect on the story, so you should try various means of appeal and burst through the IU Finals.
Regarding Ryuugu Komachi's burst appeal, there is more information under Stage Performance Tactics.
Rewards for clearing the first time:
Rewards for clearing each route:
When choosing a member of Ryuugu Komachi, if you touch their breasts at this point, each of them will react to this in a different (often amusing) way. However, this has no impact on the story at all (in other words, feel free to do it! Consider it release for all those times you wanted to do it in the main game but couldn't because it would result in bad communication.)