You don’t need to create Homepage and Blog pages if you used 1-Click Demo Data import feature or imported theme demo content manualy.
First of all, you need to create required pages and select it for frontpage display:

- Go to Pages > Add New
 - Input some page name, for example, Homepage (we will fill it some steps later)
 - Publish homepage page
 - Go to Pages > Add New
 - Input some page name for the blog, for example, Blog and Publish it
 - Go to Settings > Reading
 - Choose Front page displays option “A static page”, then select Home page that you just created for Frontpage option and Blog page for Posts page option:
 - Click Save Changes