The aim of this chapter is to offer an accessible overview for beginners seeking a foundational understanding of Primordial Black Holes (PBHs), encompassing their formation and abundance, without delving into extensive and complex equations. It is important to note that this chapter is designed to be introductory, striving to be self-contained so that all explanations and equations provided herein can be comprehended or derived by readers with a basic grasp of general relativity and cosmology, without reliance on external literature. Our goal is not solely to present quantitatively accurate facts that demand heavy computation or simulation for verification and to guide readers towards many reference papers, but rather to foster a clear physical understanding at the qualitative level. The price to pay is that this chapter is neither exhaustive nor deeply quantitative; any numerical values and associated equations should be interpreted as rough estimates.