The first step to determining the supporting details of a piece is to identify the main idea. The main idea may be explicitly stated in a topic sentence or conclusion, or it may be the overall picture that is painted by a collection of facts or details. 

Read the following paragraph about smart phones and determine which statement best reflects the main idea based on the details in the paragraph.

Every day, teenagers use smart phones to text friends. Their thumbs are always moving over the smart-phone keypad. Parents use smart phones to keep close tabs on their teenagers. Texting and tracking devices allow parents to rest assured that their teenagers are safe. Many people use smart phones to check their daily e-mail, to play games, or to get information online. These days, people are so dependent on their smart phones that they feel lost without them!