This is an introduction lesson to the Elementary/Intermediate Algebra which defines what is the real numbers set as well as different types of set notations. Besides important definitions of terms used through whole algebra there are included properties for real numbers and visual chart of real numbers subsets. I use the nestled principle to explain for students how each subset belongs to its set. It is even more powerful if you have some objects to show how each one piece is nested inside bigger one. I usually show the Russian doll "Matryoshka" with up to 6 little dolls inside of each other. Exercises I provide in this unit promote students to develop own approach to get the solution and answer problems.