Tarski has a number of different sidebar options available which you can use to customise your site.
Widgets
Sidebar widgets are flexible way of customising your blog, adding different ‘modules’ to the sidebar and part of the footer. They’re now part of the WordPress core so you don’t even have to install a plugin.
Custom sidebar file
More advanced users will benefit from being able to write their own sidebar code, without having to hack their changes back into Tarski each time the theme gets updated.
Theme hooks
As if those options weren’t enough, you can also write plugins which interface with Tarski’s theme hooks system.