The trial of constellations to my understanding is similar to rift, you currently have 4 out of 6 constellations available and each one of them is like a rift controller set. In order to level it up you need to assign heroes, the growth, gear, artifact, skill enhancements and EE will be summed as a score. And if you want to unlock more assignment slots you need to pay points that you win when clearing the boss, different difficulty will reward different points. 

There are 5 levels with buffs and bonuses similar to rift bonuses, but here is the trick. Each constellation has different buffs and effects, and for each boss you use a combination of 2 constellations. For example in the battle with Scion of Hellfire Magnar you will use Leo and Aries constellations bonuses.

Some tricks I personally use:

You can grace of growth heroes to test them in the battle.

Slot in the constellations heroes that you don't use, and make sure to equip them with a random 5 start +30 artifact

You can use immortal heroes like Elvira for example to get long immortal status effects for extra survivability

I noticed that about 2 debuffers are enough for the gimmicks in perdition mode, but if you struggle you can try with 3 of them, keep in mind that you have to balance your damage and mechanics around

And a tip for the new players, this is just a beta right now, try clearing it on a lower difficulty, and use your points to get the molagora and maybe some gear, the whales will cover the upgrades order and heroes to use later on so you can save the resources, buy the molagora and do smart decisions later when the guides go out