Open the left menu and go to Marketing > Email. The sub-menu contains Dashboard, Campaigns, Flows, Tracking, Templates, Lists, Contacts, Billing and Email Log. Once you are inside, every page also shows a tab bar at the top with Dashboard, Campaigns, Recipients (which holds Lists and Contacts), Flows and Templates so you can move around quickly.

Direct URLs: /admin/marketingcampaigns/dashboard, /admin/marketingcampaigns/campaigns/email, /admin/marketingcampaigns/flows, /admin/marketingcampaigns/trackingparameters, /admin/marketingcampaigns/templates, /admin/marketingcampaigns/lists, /admin/marketingcampaigns/contacts, /admin/marketingcampaigns/billing and /admin/marketingcampaigns/onboarding.

If you do not see the Email group under Marketing at all, the Marketing Campaigns module is not enabled on your account.