Whilst in the page editor, anywhere in the main text box to activate it and then click the Table link from the menus.
Hover over the Insert table link, which will provide you with a fly-out menu. Roll over the menu to select the number of cells and click when you are happy.
You will see that a table has been added to the text box. 
The table will automatically fill the width of the text box and the height will increase as you add content, whether text or images (see add an image to an eCreator template if you're unsure how to do this), to it.
Simply click into a table cell to edit it, as you would do with any other software.
If you need to edit the table, such as adding or removing columns, use the table options at the bottom of the table.
If you are unsure what the icons do, simply hover over them and a tooltip will help you.