As you can see, columns headers are created by ! column name. Cells are created by | cell text. The divider between rows is |-. You can add an extra column by just sticking ! new column name at the end of the last column name. To fill the cells in that column, you need to add another cell to each row: fill it by typing | cell text. If you want to add an extra row, just add |- to the table, and fill it with however many cells are appropriate.
To recap, the markup is:
{|
table start:required!
|+
table caption:optional. Only between table start and first table row
!
table header cell:optional. Consecutive cells may be added on same lines separated by double marks (!!); or start on new lines, each beginning with its own single mark (!).
|-
table row: optional on first row, otherwise required. The wiki engine assumes the first row.
|
table data cell: required! Consecutive cells may be added on same lines separated by double marks (||); or start on new lines, each beginning with its own single mark (|). Single marks are also used to separate HTML attributes from cell contents (both data or header), or caption contents.
|}
table end:required!
Blank spaces at the beginning of a line are ignored.
Escaping to insert a pipe (|) character into a table can be done using the <nowiki> markup.
class="wikitable" is used with a lot of tables on Wikipedia, and adds some standard formatting.
Using || and !! with tables
The above markup must start on a new line. This includes the cell markup (| and !). But the double cell markup (|| and !!) can optionally be used for adding consecutive cells to a single line.
For example, this would produce the same table as above:
