Sorry, but I'm very confused about the dawn era and the Et'Ada. And this is kinda my missing piece of the puzzle to become a real lore buff Any help is very appreciated.

et'Ada is the generalized term for every kind of (primordial) spirit, including gods, no matter if they're Aedra, Daedra, Magna'ge or whatever. They all represent/are a concept, like Akatosh is time, for example, or Mehrunes Dagon is destruction, or the Redguard pantheon which has a tiny, little god for really just about every issue you can think of. Because they represent concepts, the et'ada were the first inhabitants of the Aurbis (the TES 'universe'), as the Aurbis started out as a space of ideas (which the et'ada are - as said, the spirits/gods are their concepts) before becoming more material. Some et'ada are more aligned with Anu (stasis) and others more with Padomay (change). Later, during the creation of the world, they split into the three main "tribes" - the Aedra, who took part in the creation of the world, the Magna?ge who fled during the process, and the Daedra which never took part. It is classically said that Aedra are more Anu-aligned and the Daedra more Padomay-aligned, but that doesn't need to hold true for everyone of them.

The Dawn Era is... well. You know how time usually works, right? One thing happens after the other, in orderly linear fashion. Moreover, one thing causes other things, in an orderly chain of causality. Well, in TES this linearity and causality had to be established first, at the Convention (of the Aedra) at Direnni Tower. Before that, time was unordered and a-causal: Several contradictory events could happen at the same time, and in no clear chronological order, either. That is why there can be no clear history of the Dawn Era: Because several contradictory accounts of what happened are all true at the same time! This state of affairs now and then happens again in so-called dragon breaks ("dragon" standing for Akatosh, i.e. time), the most famous one being the Dragon Break which lasted 1008 years in the First Era. During that time, several contradictory events happened at once with no clear chronological order, too. But before the Convention, in the Dawn Era, that was normality.

It should be noted that there is a certain power in Dawn time. If you aren't constrained by causality, you can do quite much. That is why Dawn Magics are the most powerful kind of magic in Tamriel. The Thalmor are said to have mastered them. Furthermore, every instance of apotheosis seems to be associated with a dragon break. For example, when the Tribunal ascended to godhood, there was a dragon break, since now they had always been gods... and at the same time had just become gods. That's probably also the reason for all the conflicting accounts of the Battle at Red Mountain: Might be they're all true, because a dragon break happened there.

Thx! But I don't understand Lorkhan's plot. All parts of his plot happen at thr same time, but somehow, it wouldn't, right?

No, Time already exists. Akatosh exists, so time does. Aurbis already knows chronological orders of things; but it won't always be the right order, and causality will not always be held.

In fact, the creation of Mundus can maybe serve as an example of how the Dawn Time works: Elves claim Lorkhan tricked the other et'Ada. Men claim the other spirits followed voluntarily. And, since it happened in the Dawn Time, both may be true. View it in term of narratives: You can form a narrative that says Lorkhan tricked the spirits and you can form a narrative that says one that says he convinced the spirits. And even those two narratives contradict each other, they may be both true. But you cannot form an overall narrative of what happened in the Dawn Time because, well, if you look at all the stuff that probably happened there, it contradicts each other.