The Single Text Field question type allows the respondent to type their answer into a single-line text field. You can restrict the response length or match it against any number of validation options, such as making sure it is a proper email address.
The Single Text Field serves a range of simple tasks for retrieving your respondent's data. You'll want to use this field to get their name, phone number or any other short text you want to collect.
[edit] 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.