.rar is a compressed archive, similar to a .zip. This happens by default when our transfer to you is a large size. To "un-archive" the .rar you will need a free software:
MAC users: Download THE UNARCHIVER
PC users: Download WINRAR
Once you've uncompressed the .rar, you will most likely get a .zip. Simply un-zip that one as well, and you'll be able to access the files we sent.