There is a really easy way if you have Microsoft Word.
First create your table in Microsoft Word.
Then highlight the table in Microsoft Word and Copy it to your clipboard.
Then go to your page in WordPress and click the visual editor tab.
You will need to have the Kitchen Sink open which is the last button.
Look for the button that says “Paste from Word” when you mouse over it.
Press “Ctrl” V to paste your table into the page.
Don’t do your styling in Word because the import will strip the styling. Go to your html tab and see the markup for the table. You can add classes to the html in order to do the styling in your CSS file.