At any point in time you can save your work by the "System > save as" or ctrl+S controls.
To open an existing project press the "System > open" or ctrl+O control to load in a project, this will remove all added devices and the current grouping structure.
All devices in the opened project that are in the network will be synced and appear online. If some devices are still unpowered then they can be connected by the "Network > scan" or ctrl+F control, after power up.