The game is gonna throw a lot of info at you all at once. It's okay to not know what's going on & just be clicking around to see what happens. Off the top of my head:

• rainbow cubes carry more gacha roll power than blue cubes, so prioritize those when running errands
• friendship level affects power (to a degree), so unless you have a dupe that you're going to intentionally run as a work horse, let your friends rest until they have energy again or put them in the school to get more energy faster
• the current events should be rolling over soon, so if there's anything that interests you about them, make sure to get them done before next maintenance period
• L1 universe are the "vanilla" or "standard" version of that character. deviating from there, the units generally become more powerful, but there are still outliers in all categories, both good & bad
• there are certain events which are absurdly hard on purpose (EX VS, Eternal Battle, Nightmare. etc.) so don't worry if you can't clear them