Select the row below the rows you want to keep visible
Go to the View tab
Click Freeze Panes
Select Freeze Panes from the dropdown
To freeze the top row, go to View and click Freeze Panes, then select Freeze Top Row
To freeze the first column, go to View and click Freeze Panes, then select Freeze First Column
To unfreeze rows, go to View, click Freeze Panes, then select Unfreeze Panes