Using Custom Answers
For the Multiple Choice question you can enter the question text, then enter up to 5 possible custom answer at once for this question (further answers can be added after this is then saved).
For each answer that you enter you can set an 'Action' to add or remove the user from a Group, if they choose that answer.
You can also set chaining options for each custom answer, to skip to another part of your survey, or to toggle the visibility settings of another element (e.g. to un-hide hidden text or a hidden question).
For the Multiple Choice - Multiple Answers question, the only additional option is that you can set how many of the multiple choice answers a user can select for that question.
Link to Group Category
This option allows you to pick a category from your Site Groups and display all groups within the category as answers. This can be used for allowing users to select for themselves the groups in a category that they would like to join. Any registered users will be added to the groups that they choose automatically.
Link to Demographic question
This option allows you to pick a Demographic question and display all answer options as the answers. This can be used for allowing users to select themselves the demographics groups that they would like to join. Any registered users will be added to the groups that they choose automatically.