Giving a novice multitrack midi files with No instructions is a cruel prank IMHO!
Whoever created these tracks is the only one who knows how they were mapped. Even if they were all stock instruments, you need to know which drum kit or which string ensemble. It's kind of crazy that they didn't just print the tracks to audio like a sane person would.
Contact the creator and find out which track gets which instrument before you waste any more time guessing.
He/she should be able to tell you how to open the Score Editor too.
BTW, check to be sure they didn't include some sort of Read Me file with the midi tracks.