The "Write to Excel" command automatically exports the model data to Excel. You will see Excel automatically open on your PC when you select this option.
The "Read from Excel" command allows you to "read-in" any data-entry changes you have made from within Excel. The video link below gives an overview.
If you go to around 1 minute into the video, you will see the model exported to Excel, edited from within excel and the data read back into FluidFlow.