Tables can be used to significantly enhance the look of a webpage.

The most useful function of tables (at least in my experience) is to arrange pictures next to text. Because I have a laptop there is a very small display area, so that when I view pages on a friends 17-inch monitor, all the pictures get out of place. This problem can be solved to an extent by using a table. If you want to use html coding, examples of how to create a table can be found at Cottage Row webpage helper, but it's a lot easier just to do them in an editor such as Composer - that way, you can use the 'table properties' to set preferences.

Using tables is one way to centre text alongside an image. However, if you do this in a list then make sure you keep the table borders - it can get confusing with different-sized pictures and it looks untidy when there are uneven gaps between each section of text.
 

here is an example of text and a picture in a table - I have specified that the column widths should not be equal, which means the column with the most in will be wider =)

If you want to have text to describe a particular picture, and start a new paragraph below the bottom of the picture on the page, doing it in a table is a good idea. That way you don't have to guess how many times you should press the 'enter' key so that the next paragraph should start in the right place.
 

Here is the description of the image. The text is aligned to the top of the cell. The border on the table is transparent.

Here is where the next paragraph starts.

Tables can also be used to define the width of your page. Some pages can look really bad when viewed on a large monitor (especially if they were designed on a small one). To combat this problem you can put the whole page into a fixed-width table. That is, instead of setting the table to take up X% of the window, you can specify the width in pixels. That will centre your page on a large monitor and take up the whole of a small one.