This is a preliminary text introducing the terminology, basic concepts and tools for the next chapters. It reflects six main streams in the area. At the beginning some basic combinatorics related to words is introduced. Then several important classes of words: Fibonacci, Thue-Morse and de Bruijn words. It is followed by a description basic structures for handling texts, like suffix trees, suffix arrays and de Bruijn graphs and by some elements on text compression. The chapter ends with the important issue concerning pseudocodes of algorithms. Their presentation is done in a simple and understandable form since this is a central element of the book.