The Choose One Answer question type asks the respondent to select one of a list of choices. You can specify as many possible answers as you'd like, but the respondent can only select one.
A simple field, the Choose One Answer question type is useful for asking your respondent which choice they prefer, among other things.
Example
When selecting a question or content type, you can see what you're getting before you make your decision! Click on the Examples link at the top-right of each question type box. You'll get a brief preview of what the type looks like and how you might use it.