You can enter formulae in several ways: using the icons, or by typing on the keyboard, or by a mixture of both methods.
Click the cell in which you want to enter the formula.
Click the Formula icon on the Formula Bar.
You will now see an equals sign in the input line and you can begin to enter the formula.
After entering the required values, press Enter or click Accept to insert the result in the active cell. If you want to clear your entry in the input line, press Escape or click Cancel.
You can also enter the values and the formulae directly into the cells, even if you cannot see an input cursor. Formulae must always begin with an equals sign.
You can also press the + or - key on the numeric keypad to start a formula. NumLock must be "on". For example, press the following keys in succession:
+ 5 0 - 8 Enter
You will see the result 42 in the cell. The cell contains the formula =+50-8.
If you are editing a formula with references, the references and the associated cells will be highlighted with the same colour. You can now resize the reference border using the mouse, and the reference in the formula displayed in the input line also changes. Show references in colour can be deactivated under LibreOffice - PreferencesTools - Options - LibreOffice Calc - View.
If an error occurs when creating the formula, an error message appears in the active cell.