Activity Log automatically adds logs when events happen in concrete5.
concrete5 keeps logs e.g. when an email is sent, or when an error occurs. There logs can be found under Dashboard > Reports > Logs. Logs can be very useful for debugging purposes!
Events are triggered by the concrete5 code. E.g. when a user logs in, concrete5 triggers the event 'on_user_login'. These events are useful, because it allows other code to 'hook into'. Some events are logged by concrete5, some are not. Activity Log is meant to log more than the concrete5 core does. This gives you more insight in what is happening on your site, when it happened, but also by whom.
All supported events have a default message. It's really not necessary to customize them. But if you want, you absolutely can. You can also customize the messages with 'placeholders', see the screenshot for what that looks like.
The following concrete5 events are supported by Activity Log: