Select the row you want to freeze (the row below the rows you want to keep visible)
Go to the View tab
Click Freeze Panes
Choose Freeze Panes
To unfreeze, go to View → Freeze Panes → Unfreeze Panes
Select the row you want to freeze (the row below the rows you want to keep visible)
Go to the View tab
Click Freeze Panes
Choose Freeze Panes
To unfreeze, go to View → Freeze Panes → Unfreeze Panes