Oh and the null doesnt really mean null according to my understanding. They just use that word.
Null means, in terms of a marriage, that there never was a covenant relation.
If someone is married to another person and with or without getting a divorce, goes through a marriage ceremnoy with another person, that second action does not create a covenant relationship. That act is null as far as the Church understands marriage.
The State may accept the second act as another marriage, or may consider it to be an act of bigamy (if the first marriage was not resolved in a divorce).
The Church presumes the first marriage is a covenant relationship unless and until it is shown to not be one.
I get it that you cannot understand this - you have a lot of company. I will again reiterate: I suggested three books, and someone else suggested one of the three.
If you want to learn and understand what the Church teaches, I would urge you to buy
Annulment The Wedding That Was by (Monsignor) Michael Smith Foster. Although it is written by a Canon lawyeer, it is written for the lay person who does not want to feel the writer is talking over their head - it is understandable, an replete with examples. It starts with an example of what would come under the term of “shotgun marriage”.
Other than doing that, I am not sure anyone can satisfy your understanding, or inability to understand decrees of nullity.
Sacramental Theology is a very deep area of study, We do not need to be theologians; we need to understand what the Church teaches sufficient to be able to follow Christ. Ad all too often, people come away with what might be termed a shallow understanding of the sacraments. As long as they operate on faith and the willingness to follow what Christ taught, and to seek forgiveness when they fail to do so, no more is required.
However, the Church has had 2,000 years +/- to reflect on what Christ taught, and a part of that is sacramental theology, and specifically what is marriage and what is covenant. The Church gets into the depths of a sacrament, and to many people, it simply seems to be getting “out in the weeds”, as it is very unfamiliar territory. The laity are not required to know the territory the Church is responsible for, but when there are reasonable explanations (and in the case of the book recommendation, 189 pages plus a glossary, notes (including the Canon law sections) and an index of popular names and subjects treated. It is well done - I again recommend it, if you want a thorough and easy to read explanation of what the Church teaches. Amazon has it at $16.79 new with delivery by Monday with Prime, and used starting at $1.98 and up.