As the title suggests, this exercise focuses on improvisation using only the notes C, F, and G. If you have already studied the beginner improvisation exercises, you will notice that this exercise is an extension of those exercises because the right hand now plays along with the left hand. I have included an example for you to learn; however, the main focus is for you to improvise yourself.
Start slowly and think simple. Relax your mind and focus on letting the music flow out of you; don't let your mind get cluttered with details. Listen to what you hear in your mind, and sing as your play your melody. As you feel more comfortable, add more rhythmic variations into your playing, change the bass line more often, or increase the tempo gradually. Have fun with these exercises! If you begin to feel frustrated, take a short break and let your mind clear. Come back and see what new music you can create!