If your studying Avionic then these instruments are mainly electronic devices. I am not sure what your course consists of, but if your studyng on how to repair these devices then an understanding of elctronics is essential. This is where Multisim can help. You can enter circuits into it and simulate them to further your understanding of electronics. You could eventually use it to design your own circuits once your foundation is established in the basics of electronics. Who knows you could even eventually design you own Avionic instruments. The possiblities are endless.
As far as your second question. Most books come with either a limited or demo version of Multisim. This gives you access to it to run the circuits that came with the book or to do node limited designs of your own. Unfortunately, you would have to purchase a package from NI to get a serial humber and then activate it. This is what I know and if the NI Team has something different then they will have to let you know.
