Left Turn:
In order to let traffic know that your intentions are to turn left, extend your left arm out straight (kind of like your going to give someone "five" if they are coming towards you).
Right Turn:
To let traffic know that your intention are to turn right, you have two options. You can either do the same signal that you did for your left turn, just make the signal with your right arm. Or, you can put your left arm up in a square (kind of like the boy scout sign, but giving a "high five") with your hand open.
Stop or Slow Down:
To let traffic know that your intentions are to stop or slow down, extend your left arm down with your hand open (kind of like your giving someone behind you a "down low" five).
After completing these signals, make sure to place your hand on the handlebars again to complete your turns to give you more control.
Stay safe and enjoy the ride!