The rotation manipulator
< SFM
To adjust an object's rotation, click the rotation manipulator button () in the lower-left corner of the viewport, and then drag one of the axis rings that appear around the selected object (green, red, or blue). Drag the outer light blue ring to rotate the object in screen space (the ring turns yellow when you hover over it). Drag in the middle of the manipulator to rotate in multiple directions simultaneously.
Tip:If you want to align the rotation rings to the world instead of the object, hold down ⇧ Shift when you click the rotation manipulator button. You can also temporarily align the rotation rings to the world by pressing ⇧ Shift+E while using the rotation manipulator.