An Assistant Professor is an academic rank used in most of the universities in the U.S and Canada. It is generally taken after you have earned the Doctoral degree and hold one or more postdoctoral positions. It is below the rank of associated professor.
Yes, often times there are hundreds of applicants applying for one single position. Not only the competition, but also the process itself is often very long. You have to get your doctoral degree and after more years, you will get an assistant professor position if you are lucky.