Please help us to help you:
1. Which device are you using? (A desktop or laptop computer? An Android phone or tablet? An iPad? A Windows phone or tablet?)
2. Which browser are you using? (Internet Explorer? Chrome? Firefox? Safari? Something else?
3. Where are you entering text? (Into the address bar at the top of a web page? Into a search engine -if so, which one?)
Without such information, we won't necessarily be able to provide the correct answer. However (just to show that I really would like to help) I'll take a guess that you're using Internet Explorer and that you'd like to disable the 'Auto-Complete' function. If that happens to be correct, see here:
http://www.computerhope.com/issues/ch000604.htm