Activity web part is a modern UI web part which is available in SharePoint modern UI pages, you can add a modern ui page in classic team site.
The modern activity web part shows the activities on the site from different users which include add/edit documents, creation of new list and libraries etc. You do not need to do any configuration on the web part, just drop the web part on the page and it will start showing all the recent activities.
Adding Site Activity web part
- Open a modern UI page in Edit mode, or click on Edit link available on top right of the page (make sure you have the required permissions.
- On Edit page, click on the + icon shown in above screenshot. This will open up a small dialog list different web parts for modern ui page.
- You can select by navigating to the Site Activity web part or by can also search through search box.
- It will load the recent activities on the site, you can save the changes or can also edit web part properties to show number of items/activities to be shown in Site Activity web part.
- Save all the changes and publish the web part.