The More info text box, found in the Advanced options of a question editor, allows you to add further information to your questions. This could be used to, for example, explain a particular term that is used in the question or provide a link to an external website.
More info text is not displayed to respondents by default. If you provide information in the More info text box, a 
More info button is added to your question, directly below the question text. You cannot see this in the survey builder but you can view and test it by previewing your survey. When your respondents click on 
More info the additional information is displayed.
If additional information should be visible to respondents by default, you should use the survey builder to add a note to the question instead.