Generally, a beginner should not start with M/G/--. It is better for a beginner to start with M/M/--, for which one can write differential-difference equations. However, the topic M/G/-- is usually included in most of the Queueing books in the market. For instance, Haghighi & Mishev (2008, p. 108), Queueing Models in Industry and Business, Nova Science Publishers, new York, or Jain et al. (2007), Acourse on Queuein Models, Chapman & Hall/CRC.
You are quite welcome. By the way, there is one more book that is very popular: Fundamentals of Queueing Theory by Gross and harris, John Wiley & Sons, Inc.