The slow motion mode on the Galaxy S6 lets you record videos up to 1/8 slower than the real speed. Record slow motion on Galaxy S6 (and specify which part of the recording should played back in slow motion), by doing as follows:
1. Open the Camera application on your Galaxy S4 and make sure the Rear camera is active
2. Tap the Mode button on the bottom left and touch the Slow Motion option
3. Now start recording your video
4. When finished, tap the preview icon on the bottom right to view to recorded video
5. Now, tap the Slow Motion icon to watch the video (By default, it randomly plays some part of the video in slow mo mode)
To precisely specify which parts of the video should be played in slow motion, do as follows:
1. Stop the play back
2. Use the start bracket and the end bracket to specify the area and then drag the white circle in to that area
3. Tap the slow motion section and there you have 3 available options: Split, Speed and Delete
4. Touch the option you need, make necessary changes and when you are finished edition the video, tap the Export button on the top right to save the edited video