In the bottom left hand corner you should see either a triangular arrow pointing right (the ‘play’ button) or two parallel upright lines (the ‘pause’ button).
You might want to pause on some written parts to give more reading time. You can also use the space bar on your keyboard which will switch you between play and pause.
Immediately above these buttons there is a progress bar. The proportion of a video you have watched is shown as a red bar and unwatched is grey. Where you are now is shown by a small disc which can be dragged forwards or backwards along the line and released. It will start to play from wherever it is released, so if you didn’t quite catch a bit and want to replay it you can drag this back a small way.
Using the left arrow button on your keyboard will take you back by 5 seconds per press and the right arrow button, forward.