At the bottom right of the window you can see the controls for the Onion-Skinning function of the image editor. What onion-skinning means is that in a single frame of any sprite animation, you can choose to see any of the preceding or succeeding four frames as a semi-transparent layer under the image frame you are currently working on.
You can choose the alpha value that each frame will be drawn with, from 0 to 255, as well as how many of the frames to show. By setting the Forward value you can see those frames that come after the frame currently being edited and by setting the Backwards value, you can see those that come before. You can set these to a value from 0 (none) to 4 (all four frames will be drawn), permitting you a far greater control over animations and positioning than was previously possible.
Note that we suggest using the onion-skinning over a colour-fill background rather than a transparent one (you can set this option from the View menu of the image editor and selecting Set Transparency Background), as it makes the transparencies of the various skins easier to see.