The columns you see depend on the columns you display or hide.
Group by Category 
Groups history messages into categories. The available categories depend on the messages currently in System History, but can include Job Settings, Storage, and so on.
History Starting
Use this list to filter the date range of history messages shown in the System History window.
Description
A short description of the action taken. For each action, the description includes a number at the end of the text indicating the number of detail items listed for that action. You can expand an action to view its details.
User Name
The logon name of the user who initiated the action.
Time
The date and time that the action or process was initiated.
Severity
Indicates whether the message is for information only, or is an error or warning.