Hovering over a line will display a tooltip with the changeset which last modified the line. You can then right click a line and select 'Show Changeset Details'. This will display a dialog with the changeset details. Alternatively you can right-click a line and select 'Launch Changeset Dialog...' to display the Changeset Dialog as described in the section called “Changeset Dialog”.
Use the 'Legend' toolbar button to see what each colour represents.
With a line highlighted, use the 'Changeset Information' toolbar button to see more detail.
Use the 'Show Line Numbers' toolbar button to see line numbering on the left.