Demo Content doesn’t contain WP Options and Widgets, so you need to insert them manually via Appearance -> Widgets. Here are a few examples how to do this:
For example, in order to add Photo Gallery, you need to install Instagram Feed plugin and set it up. Then you will be able to add its shortcode via standard Text widget.
MailChimp Sign-Up Form also needs MailChimp for WP plugin to be installed and set its API up in order to work properly.