Miku MIku Dance (MMD) is a 3D animating programm., witch is used to make models dance, pictures or even to make short movies.
you need pmd editor (and several tutorials XD)
PMD Editor is an application for MMD (Miku Miku Dance) where you can edit the models
.mqo is for metasequioa, Metasequioa is a program that can be use to create MMD models.
If you are using the regular MMD (miku miku dance) you cant but if you are using a multi model edition of MMD you can download new models.
It stands for Make My Day, but on YouTube it commonly stands for Miku Miku Dance, which is an animation software.
yes its a common bug
You can use google images or make your own
You can get them on Youtube, Nico Nico Douga, VPVP wiki, Deviantart and many more places just look and you'll find what you need.
Download the program on this site: http://www.geocities.jp/higuchuu4/index_e.htm Now, simply use the program to make a miku hatsune video!:P
If you are using the MMD multi model edition they should be in your MMD[insert version of MMD you are using] → UserFile → Model
You use their bones to move them through frames to make motion data. I would suggest looking through tutorials if you're a beginner, I've provided one link below in the 'Related Links' section.