To name a frame and then jump to it, click on the frame on the timeline and type in a name in the properties.
In the movie on the right, frame 15 has been named "middle"
The movie will play to the end, at frame 26 and then the script has been added:
so it will not go all the way back to the beginning and restart, but will go to frame 15 and repeat from there. This is very convenient if you add or delete frames later and frame 15 is no longer the middle frame.