The grid exists in an invisible space between each cell. Each cell also has a border, which is its boundary. You can highlight cells, columns and rows by displaying the border. Either create a style, based on the table style, or apply an effect to the cells you want to change.
The default style for tables is a black grid surrounding every cell.
The example and template files on the examples disc contain several different table styles which you can use in your own document.
See: