Open the toolbar's site-name menu and click a link by its visible text (e.g. the "Pages...", "Users...", "Administration...", "Aliases...", or "User settings..." entries). Matching is case-insensitive and ignores a trailing ellipsis, so "Pages" matches "Pages...".
Most of these links carry data-rel="sideframe": django CMS opens them in an in-page iframe overlay (.cms-sideframe) rather than navigating the main page. Assert on the sideframe with the step below, not with webship-js's generic "I should be on ..." page-URL steps.
Examples
When I click "Pages" in the CMS toolbar menu
When I click "Users" in the CMS toolbar menu
And we click "Administration" in the django CMS toolbar menu
When I click "User settings" in the toolbar menu
And click "Aliases" in the CMS toolbar menu
Pattern
When(/^(I |we )*click "([^"]*)" in the (?:(?:django )?CMS )?toolbar menu$/, …)
Part of @webship-js/django-cms-steps (github.com/webship/django-cms-steps), a step pack for Webship-js 2.0.x.