Please check both sentences and let me know what exactly difference is between both sentences.
It (a movie) does not get released
It (a movie) does not release.
Maulik has given you a good start. What you need to think about are the practical difference between the two options. The clear difference is "get". So what does "get + past participle" give us?
Well, firstly, movies don't release themselves! But I think you knew that. So our second option is not great, as we can't use "release" as an action of the movie itself. For this to work we would need a verb that can be something that a movie does.
If a movie doesn't suck.
Moving on to "get", in your first sentence; this sentence is perfect - it sounds natural and is entirely self-explanatory. "Get" is an extremely flexible verb with many uses and meanings. Its function in this case is to externalise the action. That is, we are saying that the action "occurred" without explaining how, and more importantly by who. This is a form of the passive/causative, which is a vital tool in English.
We use "get + past participle" to externalise an action where the "agent" (who did it) is unknown, unimportant, or self-explanatory. Here are a couple of other examples:
When a book gets published, it is a nervy time for the author...
If you get arrested, it's important to know your rights...
In the event that you want to explain who performed this "externalised action", you can do so by simply using "by":
If a movie doesn't get released by a movie company, it's likely due to...