Students Creating and Emailing Worlds

Hi,
I would like to have my students create worlds and present them in my classroom. If they create their world on their home computer, can they email them to me? If so, why do they always open in a zip file? Can PC worlds transfer to MAC worlds? I am just confused about how to get them to work on them at home and then be able to present in school off of my classroom computer. Any ideas?

Thanks!