The scenario creation (only available for the quantitative questionnaires) allows your respondents to only see a set of questions based on their answers to previous questions. Therefore, you can define that a respondent will see the question #5 only if he answers "Yes" to question #4. The number of scenario within one questionnaire is technically unlimited. However, it is advised not to create too many. Otherwise, you may discourage your respondents.

We talk about a node to indicate the start of a scenario.

From a node, several branches can start based on the answer that has been given. A scenario can start only from a Single-choice or Drop-down list question. It is only with those 2 question types that the given answer is known in advance and unique.