Here you will find links to websites about music and musicians that are suitable for English language learners.
This Simple English Wikipedia page is a good place to start for brief information the different styles and instruments of music through the ages.
BBC's Music Magazine has this page containing brief texts on The 50 Greatest Composers of All Time.
This great page from Wikipedia has brief information about and pictures of all the musical instruments in the world. It links to more detailed information about those instruments.