You can use cells with text to refer to the rows or to the columns that contain the cells.
In the example spreadsheet, you can use the string 'Column One' in a formula to refer to the cell range B3 to B5, or 'Column Two' for the cell range C2 to C5. You can also use 'Row One' for the cell range B3 to D3, or 'Row Two' for the cell range B4 to D4. The result of a formula that uses a cell name, for example, SUM('Column One'), is 600.
Automatically finding labels is a legacy feature and deactivated by default as it can produce nondeterministic behavior depending on actual document content. To turn this function on, choose LibreOffice - PreferencesTools - Options - LibreOffice Calc - Calculate and mark the Automatically find column and row labels check box.
Using defined labels instead is always possible and behaves similar but in a defined way.
If you enter a label name in the formula yourself, enclose the name in single quotation marks ('). If a single quotation mark appears in a name, you must double it, for example, 'Harry''s Bar'.