Merging Cells

To merge cells do the following:

Make sure that you are in Row and Cell editing mode.
Select a corner cell from the cells you want to merge by clicking on the data area of the cell (as shown below):
Select the other corner cell of the cells you wish to merge by holding down the <Shift> key and clicking on it (as shown below):

Alternatively, you can press <Control> and click a cell you wish to add to the selection (Control+Clicking an already selected cell will remove it from the selection).
Another way is to press the mouse button on the first cell, then drag the cursor over to the other end of the cells you want to merge before releasing the mouse button, which will select all the cells between them.
Right click on one of the selected cells and select Merge from the menu (as shown below):

Note that if you want the cells to be merged on the output format, you can set the appropriate option in the Settings Dialog.