When you see this symbol in the top right of a grid, it means that a barcode scanner can be used on it:
To peform a search using a barcode reader, just click once on the grid to put the focus on it, then scan a barcode label. If a corresponding item is found in the grid, the add/edit window will open to let you edit the details.
In some windows you will find this kind of frame that will let you do a search using a barcode scanner:
Just place the cursor in the "Barcode" text box then scan a barcode label. If an item is found, it will be automatically selected in the drop down list below the barcode text box.