Activities - Tasks, Events, and Calendars

Activities includes tasks, events, and calendars. 

Tasks-

This is to keep your to-do list in Salesforce. You can relate tasks to records for leads, contacts, campaigns, contracts, etc.. Tasks are assigned to specific Salesforce users and can be either single or recurring tasks.

Events and Calendars -

This is to track meetings with customers, prospects, and colleagues. Tis is to track meetings with customers, prospects, and colleagues. Drill down from events to related records, feeds, files, contracts, etc.. You can also track events in reports.

Visual: https://www.youtube.com/watch?v=lLqIJmWFnoI

Reference:

https://help.salesforce.com/s/articleView?id=sf.activities.htm&type=5

https://help.salesforce.com/s/articleView?id=sf.tasks.htm&type=5

https://help.salesforce.com/s/articleView?id=sf.events_and_calendars.htm&type=5