CampaignAmp defines the difference between Diary and Task Events as:

Diary Event: Something that is happening at a certain time and place ie. a Live event or a Promo event like an interview or TV show.

Task Event: An activity that needs to be completed by a certain time.

Double click on any date in the diary to bring up a window where you can select the type of event (Diary or Task) that you would like to add and follow the steps.

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