Open the add form of a content type (/node/add/<type>), by machine name or by a label that maps to it ("Basic page" becomes basic_page; pass the machine name when the label differs, as page does). Pair it with webship-js's field steps and the rich text editor steps to fill the form, and with "submit by id" to save it.
Examples
Given I am adding an "article"
Given I am adding a "page"
Given we are adding an "article" content item
Given I am creating a "page" node
And I am adding an "event"
Pattern
Given(/^(I am |we are )*(?:adding|creating) an? "([^"]*)"(?: content item| node)?$/, …)
Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.