You can read the very short "History of Classical Music" accompanied by music examples from the Naxos site.

You can also learn the basics about "Musical Instruments" from the Naxos site.

You may wish to enhance your knowledge of classical music by attending the free coursera course "Introduction to Classical Music" by the Yale University Professor Craig Wright.

Follow the twenty three hour-long free video lectures on "Listening to Classical music" by the Yale University Professor Craig Wright