Failed to load scene after copying project

Hi! After I have exported a project file to a friends laptop he opened the project, but failed to load the scenes. We had this problem before. It is the first time working on a team so we don't have much experience on that. Can any of you recommend a software like github that is compatible with unity? Is there any way how we can restore the scenes? Luckily we made backups, but there is still valuable work lost...