As Clive mentioned, on the far left you'll find a menu of things you can do
for editing. The bottom one, Pre, is the one on which you click when you
want to start a table.
Everything inside the [ pre ] and the [ /pre ] will maintain the desired
spacing once you either preview or post the document. So, all the columns should line up.
Note that the very first line following the [ pre ] has an indent, so it's best to start your column headings in the next line and use that first line for a title.