On this site, the defined page regions where you can add page extras are…
left– the left columnright– the right columntop– an optional area across the top of both the centre and right columns
In addition, the Home page has two further areas defined…
bottom_right– an optional area across the bottom of both the centre and right columnsbottom_full– an optional area right across the bottom of all three columns
And don’t forget that you can place most of the widgets anywhere in the main text area of the centre column by using the shortcode system.