If you have a spreadsheet with lots of data, scrolling usually makes the header disappear. LibreOffice can lock rows or columns or both, so they remain fixed as you scroll around.
To freeze a single row or a single column, proceed as follows:
Procedure 11.6: Freezing a Single Row or Column
To create a frozen area before a row, click the header of the row (1, 2, 3, ...).
Alternatively, to create a frozen area above a column, click the header of the column (A, B, C, ...).
Select View › Freeze Rows and Columns. A dark line appears, indicating the frozen area.
It is also possible to freeze both rows and columns:
Procedure 11.7: Freezing Row and Column
Click into the cell to the right of the column and below the row you want frozen. For example, if your header occupies the space from A1 to B3, click cell C4.
Select View › Freeze Rows and Columns. A dark line appears, indicating which area is frozen.
To unfreeze, select View › Freeze Rows and Columns. The check mark before the menu item disappears.