This theme supports multiple sidebars and they are all dynamic. This means that you can insert whatever widgets you like on them.
There is one default sidebar that goes to each of the pages. If you would like to have more sidebars than the default one, then you can create your new sidebars in Gossh Options » General » Sidebars section:
To customize your sidebars you have to go in the admin panel » Appearance » Widgets. In this section you will see your sidebars on the right part of the page. Now you can drag and drop widgets from the left into your sidebars.
Here is an example of a sidebar
You can assign a custom sidebar to each page in the “Page sidebar” field of the Page Settings section.