From the spectra of hydrogen to the cosmic showers, and the gamma ray bursts, several interesting concepts of nuclear physics are discussed in the useful notes that are dedicated to all levels of readers. Basic information purview is done keeping in mind the beginners as well as the intermediates. Upper undergraduate basic essentials are demonstrated too. In the first chapter all the knowledge base has been served in order to give an idea about what systems theory is all about. This basic information makes the useful notes perfect for beginners. The second chapter talks about various applications of systems theory to serve you with practical knowledge. In the last three chapters, the development and history of systems theory is described. This is a complete package for basic concepts of systems theory. You can refer to high level useful notes once you have acquired basic knowledge base. Systems theory is a complex subject to understand all at once. The useful notes explain how to include every small detail related to the general theory of systems. That is why we used precision while dividing the content into chapters. All interrelated information is compressed within a chapter so you will not require switching between chapters now and then.