By setting colspan to "3", the cell in the first row spans three columns. If we instead had set colspan to "2", the cell would only have spanned two columns and it would have been necessary to insert an additional cell in the first row so that the number of columns will fit in the two rows.
In the example above rowspan is set to "3" in Cell 1. This specifies that the cell must span over 3 rows (its own row plus an additional two). Cell 1 and Cell 2 are thereby in the same row, while Cell 3 and Cell 4 form two independent rows.
Confused? Well, it is not uncomplicated and it is easy to lose track. Therefore, it might be a good idea to draw the table on a piece of paper before you begin with the HTML.
Not confused? Then go ahead and create a couple of tables with both colspan and rowspan on your own.