When you merge two or more adjacent cells, the content of one cell is spread over the other cells, as shown in the following example.

Text spread and centered over multiple cells

You can split a cell that has been merged but you cannot split an unmerged cell. You can, however, split the contents of an unmerged cell and divide it across other cells. You can also merge the contents of separate cells by combining it into one cell.

Merge cells

Important  - Only the data in the upper-leftmost cell of a range  (range: Two or more cells on a sheet. The cells in a range can be adjacent or nonadjacent.) of selected cells will remain when the cells are merged. Data in other cells of the selected range will be deleted.

1. Copy the data you want to display in a merged cell  (merged cell: A single cell that is created by combining two or more selected cells. The cell reference for a merged cell is the upper-left cell in the original selected range.) into the upper-leftmost cell of the range of adjacent cells you want to merge.
2. Select the cells you want to merge.
3. Click Merge and Center on the Formatting toolbar, which will merge cells in a row or column and center the cell contents.
4. To change the text alignment in the merged cell, click Align Left or Align Right on the Formatting toolbar.