Click one of the categories that you would like to view. Each playlist has a few videos embedded already, you can select which videos you’d like to watch in each category by clicking the three bars with a play button icon at the top left corner that looks like this.
When you clicked that button, it will pop up a list of different video titles for you to select and watch or you can simply click the play button to watch all the videos in order from first to the last in each category.