The Decision type question can be used to add logic into your survey. Although they can be used for single page surveys to link to another part of the page, they are most effective when used on multi-page surveys.
The decision question is basically a SingleSelect question to which each response may be given a page further on in the survey which it will jump to when it is selected. In this way you can choose to jump over questions in the survey.
The Decision question should be the last or only question on the page it is used on.
All Decision questions are made mandatory, to ensure that the flow of the form is maintained.