I've worked in client side businesses with marketing teams of 5-30 people, two of those in marketing. A lot of the day to day the marketing teams do is manage outside agencies who do the creative, ad-buying, events and present that up to the stakeholders. There obviously is strategy work which is pre-campaign and is what the more senior marketers do (even though this is the most emphasized part in uni.) There are a few more functions which are more likely to not be subcontracted like CRM (emails), content (blogs etc), analytics, social media management and corporate comms.

For your original question, the difference between this and advertising is an advertiser receives a brief and builds creatives appropriate to whatever channels they and the marketer choose.

This is my experience and a few marketers have disagreed with this - obviously it varies between companies.