Multi Actions are not actions in themselves, but instead, are collections of existing actions. This is ideal for scenes - turn on the TV, lower the hallway lights and turn off the living room lights, for example. Another example is linking a Geofence Attribute to a Multi Action that turns off everything in your house. To select the actions you want to combine in the Multi Action, just tap them to select them, a number will appear, showing the order the actions will be called in. To deselect an action, just tap it again.