What content to use for inserting images

Images (and other media) in WordPress are stores as attachments — which are a special native post type (more or less).

There are two common ways to display attachments in a post context:

  1. Include them in post content (individually or via gallery shortcode)
  2. Select one as featured image (aka post thumbnail) and have theme with support of the feature display it separately from content

So unfortunately natively there isn’t a way to select multiple images with intent of displaying them separately from content.

However it is a common feature in custom fields frameworks. They often offer nifty interface options for it and store attachments IDs in post’s meta data, from where it can be retrieved and used.

Personally I favor Meta Box, but there are literally dozens of alternatives floating around.