I've just started
take it slow and use the forum search - most 'problems' and false expectations with Twenty Eleven have been addressed already by this forum.
there is no sidebar in static pages in Twetny eleven - by design.
same for single posts.
there is however a page template with sideber (Sidebar Template), which you can use under 'Page Attributes' - 'template' when you edit a page.
alternatively, try the plugin http://wordpress.org/extend/plugins/twenty-eleven-theme-extensions/
if you consider customisations which include editing templates, strongly consider to create a child theme first, to make the customisations with; http://codex.wordpress.org/Child_Themes
for pure css edits, consider using a custom css plugin; http://wordpress.org/extend/plugins/search.php?q=custom+css