Know that numbers that are not rational are called irrational. Understand informally that every number has a decimal expansion; for rational numbers show that the decimal expansion repeats eventually, and convert a decimal expansion which repeats eventually into a rational number.
Please watch both videos before answering questions.
Introduction to Irrational Numbers (what are they?)
One of the many methods of estimating (approximating) the value of an irrational number.
Source: Scott Malone