I highly recommend the free podcast called Latinum (on iTunes). But it is not an overview of Ecclestiatical Latin … rather it is a podcast for truly and deeply learning the Latin language.
It will help you understand grammar and develop a vocabulary that you could then use to understand ancient Roman writings, the Mass, the Divine Office, the Latin Fathers, the writings of Newton and other scientists in Latin, etc etc.
For something more specifically ecclestiatical, I like Dr. Collins’ A Primer of Ecclestical latin.