These form the basis of western music. C major is the easiest scale to learn since the names of it's notes are just letters in the alphabet and there are no sharps or flats. On the keyboard these are just the white notes. It is frequently convenient to talk about the notes in a major scale by number. There is no need to ever count beyond 13.
All notes can have several names.
Our choice of which one to use is based on the context. B and Cb are the same note. While this may seem to be overly complicating things, we shall see later that it actually makes things easier. I'm assuming that the basic sound of a major scale is already in your ears. Make sure you can sing a major scale up and down.