Entries Overview: Add Field Columns
You can configure the columns to display using the little cogwheel icon at the bottom (below the list of sections):

This will open a modal window allowing you to select the fields you want to display in the table for each section. You can also rearrange the fields using drag-and-drop with the little handle icon to the left of the field name.
As a sidenote, this modal also allows you to reorder the sections in the sidebar, and use your own headings instead of the default headings for channels and structures.