You can change the width and the height of the table cells by changing the height and width attributes of the blank image. Since it is a blank, it will not make any difference how big or small you make it.
In the <table> tag, you will see border="1". Try changing the number to "5" and see what a difference that makes in your table. Do you see how big the border around the table got? If you change the number to "0" the border will disappear.
The cellspacing attribute that you see in the <table> tag indicates how much space is between the cells of the table. Change that from "0" to "5".
You can think of a table cell like a box. Cellspacing is the area around the outside of the box, and the cellpadding is the space inside of the box between the cell walls and contents of the box. Replace one of the blank images with some text, like "tables are fun".
You will see that there is no margin around the text that you put in, and it is right up against the wall of the table. Change the cellpadding to "5" and see what a difference that makes.
What if you want a different colored background in your table? Just add bgcolor="" to the <table> tag. Put in bgcolor="#C0C0FF" and see that you now have a blue background in your table.
Would you like a different colored border around your table? Add bordercolor="#000080" to the <table> tag, and you should have this: