As you type into the search box, Google Suggest guesses what you're typing and offers suggestions in real time. This is similar to Google's Did you mean? feature that offers alternative spellings for your query after you search, except that it works in real time.
For example, if you type bass, Google Suggest might offer a list of refinements that include bass fishing or bass guitar. Similarly, if you type in only part of a word, like prog, Google Suggest might offer you refinements like programming, programming languages, progesterone, or progressive. You can choose one by scrolling up or down the list with the arrow keys or mouse.