Use campaigns to store all your marketing information and activities, and to measure the success of your efforts. Campaigns contain planning tasks and campaign activities you need to manage for the marketing campaigns.
In Dynamics 365
Dynamics 365 has two types of Campaigns. Normal campaigns and quick campaigns. Microsoft has provided this diagram explaining the difference between the two.
Standard campaigns are used for managing the end to end process of a complete campaign process allowing for multiple marketing lists and activities to be included in the campaign. Quick campaigns are used for distributing a single activity to contacts, accounts or leads or to a single marketing list.
Quick Campaign example would be sending out a newsletter to a single marketing list.
Campaign example would be created a Campaign for a trade show, where leads and contacts are invited, attendees are tracked, new leads are found and post trade show activities are sent to the attendees.
See https://docs.microsoft.com/en-us/dynamics365/sales/get-started-app-marketing-sales for details on Dynamics 365 Sales App Campaigns.
See https://docs.microsoft.com/en-us/dynamics365/sales/create-quick-campaign-using-app-marketing-sales for details on how to create quick campaigns in Dynamics 365 Sales App.