To use conditional tags with widgets, you need to install additional plugins like Widget Logic or Widget Logic Visual
For example, if you put
is_single()
in widget logic, then it displays that widget on single posts only. Likewise if you put is_page(), then the widget will be displayed on pages only. Read more info here – http://codex.wordpress.org/Conditional_Tags
I haven’t used Widget Logic Visual yet, but people say it’s more convenient than Widget Logic for end users.