In Smart Mode, all you need to do is specify the campaign basics (goals, website, targeted locations, keyword themes, ads, and budget) with suggestions from Microsoft based on your business website. Microsoft Advertising will take care of the rest.
In Expert Mode, you will specify all details of a new campaign (ad copy, keywords, bid strategy, budgets, audience targeting, location targeting, day of the week, time of day, device, etc.) You can also import campaign data from Google Ads and Facebook Ads.