I can do it it since it's the easiest section:
This is the Gachagacha section. I took a screenshot on the section you'll use the most - the Friend Point Gacha. Friend points are gotten by doing lives and picking one of your friends to help when they prompt you. Also I think they just give you friend points because they just seem to give them away like Candy (I currently have 24,000 Friendpoints O.o)
Anyway, the little treasure chests at the bottom are the current Gacha promos they are also doing - right now it's just the Sayu Grad Gacha so only one of the treasure chests are unlocked -- those generally need Star Stones (I have 2).
For the FP Gacha, it costs 100 friend points per card - and it seems you can only roll on Normal and Rare's. The first button lets you roll on one at a time, the second lets you roll for 10 at a time - inventory permitting of course.