This action block returns the name of the most recently interacted with item. So, for example, if the user taps an item on the screen, the name of the item that was tapped will be set into the Activity Primary Node Name.
This action block is incredibly useful. You can connect it to another block that has an item name as one of its properties. So, for example, maybe you want to hide an item when it is tapped. You can do so by using the Hide Named Item block and then connect this Activity Primary Node Name block to that name.