Addresses and References, Absolute and Relative
The cell in column A, row 1 is addressed as A1. You can address a range of adjacent cells by first entering the coordinates of the upper left cell of the area, then a colon followed by the coordinates of the lower right cell. For example, the square formed by the first four cells in the upper left corner is addressed as A1:B2.
By addressing an area in this way, you are making a relative reference to A1:B2. Relative here means that the reference to this area will be adjusted automatically when you copy the formulas.
Absolute references are the opposite of relative addressing. A dollar sign is placed before each letter and number in an absolute reference, for example, $A$1:$B$2.
LibreOffice Calc shows the references to a formula. If, for example you click the formula =SUM(A1:C5;D15:D24) in a cell, the two referenced areas in the sheet will be highlighted in color. For example, the formula component "A1:C5" may be in blue and the cell range in question bordered in the same shade of blue. The next formula component "D15:D24" can be marked in red in the same way.
When to Use Relative and Absolute References
What distinguishes a relative reference? Assume you want to calculate in cell E1 the sum of the cells in range A1:B2. The formula to enter into E1 would be: =SUM(A1:B2). If you later decide to insert a new column in front of column A, the elements you want to add would then be in B1:C2 and the formula would be in F1, not in E1. After inserting the new column, you would therefore have to check and correct all formulas in the sheet, and possibly in other sheets.
Fortunately, LibreOffice does this work for you. After having inserted a new column A, the formula =SUM(A1:B2) will be automatically updated to =SUM(B1:C2). Row numbers will also be automatically adjusted when a new row 1 is inserted. Absolute and relative references are always adjusted in LibreOffice Calc whenever the referenced area is moved. But be careful if you are copying a formula since in that case only the relative references will be adjusted, not the absolute references.
Absolute references are used when a calculation refers to one specific cell in your sheet. If a formula that refers to exactly this cell is copied relatively to a cell below the original cell, the reference will also be moved down if you did not define the cell coordinates as absolute.
Aside from when new rows and columns are inserted, references can also change when an existing formula referring to particular cells is copied to another area of the sheet. Assume you entered the formula =SUM(A1:A9) in row 10. If you want to calculate the sum for the adjacent column to the right, simply copy this formula to the cell to the right. The copy of the formula in column B will be automatically adjusted to =SUM(B1:B9).