For example what is correct "My car is getting repaired" or "My car is being repaired" , can't understand the difference , the first and the second sentences seem to be narrating about a process rather than state
See this explanation:
We use the get passive especially in informal speaking. When we use the get passive, we also place a little more emphasis on the nature of the action itself or on the person involved in the action
For me, one reason to use the get passive is to focus on something approaching or reaching an end state as a result of an action. "My car is getting repaired" emphasizes that the car is progressing toward a state of non-brokenness.
(But be careful: there are many other uses of get, including simple change-of-state/inchoative uses like "It is getting hot" or "I am getting dressed", and causatives like "I got him fired".)
The be passive is a more general way to focus on something affected by a transitive action by making it the subject. More about active vs. passive
Both sentences are correct and convey almost exactly the same information. I can't think of a situation where you could use one but not the other.
The only difference I might perceive is that "getting" feels slightly more "active" while "being" feels slightly more "passive," but this difference is very small.
The get passive can't be used with stative verbs. For example "Believe" is a stative verb. In the active voice we say
I believe you.
Or in passive:
You are believed by me.
But we can't say
You got believed by me*.
Some particples indicate a state:
John is married (Married is very much like an adjective describing John's state)
John was married last year (Unclear, is this John's state last year, perhaps before a divorce? or was the wedding last year)
John got married last year (Clear. This must be an action, and so it means the wedding was last year.
The fact that the "get" passive forces an active and specfic meaning to the participle means that it tends to be used for particular actions with surprisingly positive or negative outcomes:
She got promoted!
I got fired :(
I got told off.
You could use "was" in all three examples, but it would lose something. Using "I was promoted" is a boring telling of a fact, rather that Exciting News
In some cases the "get" passive becomes so common that it can be called a collation or even an idiom.
I'm getting hungry! (You would hardly ever say "I'm becoming hungry")