Yup, Katsuyuki-p has covered the gist of it. Had to rush off to school so I couldn't do a detailed translationthis time. I'll translate some of the finer details Katsu missed out in when I get home later.
But for now, just a few words about he'll training from my iPhone. It's a teamwork exercise and the objective is to keep pace for the idols so all three of them are jogging with the same rhythm.
Controls are: lb and rb to switch between characters, and I think A to make them jog faster and Y to slow them down. Note in the screenshots you have to manage their stamina on top of pace.
Some corrections now that I've had a chance to sift through the screenshots.
The goal in Hell Training is not so much to get your three idols running at the same pace. Instead, Hell Training for the most part plays just like all other lessons - you're basically trying to fill a meter on the upper-left-hand side of the screen, from Normal to Good to Perfect.
The only difference is that Hell Training greatly boosts all three stats (Vocal, Dance, Visual) simultaneously. However, the Hell Training option is only selectable from the scheduling menu when certain conditions are met (mentioned in Clear Blue's post). It sounds like Hell Training is entirely optional... although if the game offers you the chance to do it, why not?
To fill the meter fast, you probably want to get the girls to run as fast as they can. But running faster costs stamina. However, according to Kotori's tutorial comments in the screenshots, if you manage to get the girls to run at the same pacing, all three of them will see it as a form of encouragement and slowly recover some stamina. So I'm guessing to do well in Hell Training, you'll probably want to switch back and forth between making them sprint to expend their stamina, and regulating their pace to let them recover said stamina. If you just make the girls run at the same pacing for the entire duration, you probably won't do very well in Hell Training.
Oh, and A button to increase speed, B button to slow down (not Y).
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Some other tiny morsels of info from the Dengeki story (most of this stuff is either obvious, or something most of us already know; I've included them for the sake of completion):
-A while back the first of the 2 Weiss PR cards was revealed to sport the same illustration as the game's box art. The second card, on the other hand, will contain an illustration from the anime announcement (refer to pic in the story; card name reads "Anime wo desu yo! 76... and the rest is obscured by the other card"). Not exactly new info here though.
-Lessons will cost 1 time unit and 100 money. Choose from Vocal, Dance, and Visual lessons. There are also super lessons, which cost 2 time units and 1000 money but will last longer than the regular lessons, making it easier for you to aim for a Perfect result.
-Katsuyuki-P hit the nail with the vocal lesson. You basically hit buttons when the corresponding icons move and overlap the stationary black microphone circle thingy. By the way, in the first couple of screenshots Haruka is practising vocals alone because they depict the tutorial in the first week when you've yet to pick your unit members.
-I didn't play SP, but it seems like visual lessons in iMAS2 are exactly how Katsuyuki described them.
-For dance lessons, L and R on the panels denote left and right bumper presses, and you're supposed to press the corresponding bumper when the panels flash white, like what you'd normally do to get the flashing appeal in auditions from the original iMAS. Kotori says that the first four beats are an intro (to give you some time to adjust), and that you're expected to start pressing buttons from the fifth beat onwards. She cautions to pay attention to said intro as the tempo will change up from time to time.
-After a certain amount of in-game time has passed, your idols' casual wear will change from summer-wear to winter-wear. Alternatively, you can set summer/winter-wear in the options menu. The screenshots in this Dengeki story show their winter-wear.
-Similarly, in the options menu you can also set what the idols wear during lessons. In this next set of screenshots the idols are wearing Yoga-wear, which are Extend costumes you can purchase from the shop. Extend costumes you can purchase in shops (as opposed to DLC) include swimsuits and other lesson-wear. The Beauty Mizugi (swimwear) and Candy Lady costumes are part of the Extend selection.
