Right-clicking inside a table cell 
 will display a pop-up menu with the actions you can perform:

The table cell contextual menu provides the following operations:
Copy
Paste
Paste from Word
Save as Template
Spellcheck
Clean content
	
	Note: Read more about these options here 
 (the description is for a simple text selection, but it applies to text 
 inside table cells as well). Except for the 'paste' commands, that are 
 enabled when there is content stored in the clipboard, the others are 
 only enabled when you right-click above a selection inside the table cell.
	             
Table Operations - this entry is a sub-menu that expands while hovering the mouse cursor over. It contains operations that can be performed related to a table cell:
Increase Colspan - increase the value of the current cell's colspan attribute, merging it with the column cell to the right.
Increase Rowspan - increase the value of the current cell's rowspan attribute, merging it with the row cell below.
Decrease Colspan 
 - split the cell where the cursor is placed (if possible, meaning previously 
 merged) into two columns. If the cell colspan 
 value cannot be decreased, the following window will pop-up:
		
		
		         
Decrease Rowspan 
 - split the cell where the cursor is placed (if possible, meaning previously 
 merged) into two rows. If the cell rowspan value 
 cannot be decreased, the following window will pop-up:
		
		
		         
Add Column Before - insert a new table column before the one in which the cursor is placed.
Add Column After - insert a new table column after the one in which the cursor is placed.
Add Row Above - insert a new table row above the one in which the cursor is placed.
Add Row Below - insert a new table row below the one in which the cursor is placed.
Remove Column - remove the table column in which the cursor is placed.
Remove Row - remove the table row in which the cursor is placed.
Right-clicking a selected table row 
 (or at least two cells in the same row) will display a pop-up menu with 
 the actions you can perform:

The table row contextual menu, besides common options (7) with the table cell contextual menu, provides only one specific operation: Merge Cells. It will unite the selected cells into one bigger cell.
As you noticed, the right-click contextual menu groups together options often needed. Use it whenever you want to save time with accessing certain commands.