A cloud-to-ground lightning discharge begins with a downward moving, negatively charged stepped leader.
The powerful return stroke then follows.  The return stroke produces a bright flash of light and a loud noise (thunder).
About half of all discharges consist of just a single stroke.
The other half are composed of multiple strokes as shown below.


All of these discharges are really superimposed on each other. 
The pictures are spread out across the page here just to identify all the different processes that occur.
If you were outside and saw this flash you would see the lightning channel flicker.