In any case my best guess is that this is a student project with a deadline and they have to get this done. Therefore they don’t have time to learn to use git properly. And there’s no need for that: they must avoid merge conflicts, not solve them.
So, @Szilassi_Andras, if you and some others have made changes to the same file simultaneously, in parallel, and hope to get a working design – that won’t work . Each one of you must make changes to a file, then push them, then the others have to pull them without making any changes to that file meantime. In other words, every instance of that design file must be “locked” when it’s edited - if not in the versioning system level, then at least by your common agreement.
The same is true for a situation where one person makes changes, pushes them, then changes to another machine and continues there without first pulling. He will loose either his first or second changes, they can’t be expected to be mergeable. (Don’t ask how do I know this use case.)
Even though git is very powerful, it’s not a good fit for non-distributed (or maybe actually “centrally controlled”) development.