In a nutshell, tables create a consistent page layout. Most of you have used tables in documents that you created with a word processor such as Microsoft Word. Tables on web sites are used to present information in a particular way. Tables help designers align text and graphics in the page so that they remain in specific places and relationships to other information on the page. Tables also help determine what happens to the content of a web page when the browser window is sized.
Tables have basic characteristics and the cells within tables also have their own characteristics.
Showing borders is a personal preference, but most web sites use tables without borders, so visitors can't see them. They are there to organize the page. Most of the tables used in web page design are not visible to the visitor. You basically can put anything you want within the cells of a table. You can have another table within a table.