[1] Sidebar Single Post Layout: You can select Right / Left sidebar or full page (without sidebar). And when you select Right / Left sidebar, you are able to choose sidebar in [2]
[2] Blog Single Sidebar: There are some availabe Blog Sidebars that you can choose. And to design these sidebars, please negative to Appearance > Widgets
Here you can see the complete widgets when you choose Blog Single Sidebar [2] is Widget Area
