AggreGate SCADA/HMI gets access to PLCs, sensors, SQL databases and other data sources via Device Accounts. Every account uses a certain Device Driver to connect to a physical device, read its metadata and perform data I/O. See Adding New Devices for more information on how to create new device account.
Once a new device account is created, full synchronization of device with server will be performed. Once it's over, device should switch into normal operation state indicated by a green tick icon: 
. This state means that I/O channel data and operations provided by the device are cached by the server and may be accessed by other system facilities, such as HMIs or alerts.
If I/O channel value storage should be enabled, this can be now performed by changing History Storage Time in Device Setting Synchronization Options dialog.