You need to style tables with CSS. You can use inline CSS to do that or add styles for the table to your Custom CSS box in Design Settings. How to style tables with CSS is beyond the scope of theme support, but you should be able to find plenty of free help with that elsewhere.
Let me Google that for you → http://lmgtfy.com/?q=how+to+style+tables+with+css
If the CSS is too much for you, there are a few WordPress plugins that help you to build fancy looking tables.