You can create and modify symbols in the ArcMap table of contents for the active scenario in your analysis (for instruction on activating a scenario, see: Activating a scenario). Right-click on a data layer, click Properties on the pop-up menu, then click the Symbology tab. Note that changes made to an inactive scenario do NOT propagate to the active scenario but symbology changes made to the active scenario, DO propagate to inactive scenarios.
Create styles for your projects using the ArcMap Style Manager. Access the Style Manager dialog box by clicking the Tools menu, point to Styles, then click Style Manager.
Use the Scenario 360 Symbol Saver to create and/or apply saved layer symbology so that you can quickly change how data is displayed on your map.
For more information, see ArcMap help.