By squeezing here, it means to squeeze your fingers inwards towards the palm to form a fist. You can use a ball for this exercise or perform it without the aid of any tool. When you squeeze a ball or any other object, you are strengthening your inner intrinsic muscles. You can use a ball, towel, face cloth, or any soft object that is easy to squeeze. The idea here is to squeeze your fingers to give them the required strength. Repetitions of the exercise during the day (as and when you feel comfortable) will help to get good results.
If you have a MySquegg smart ball, then you can easily perform the exercise. You have to hold the ball in your palm squeeze it with your fingers and then release the pressure. Keep repeating the exercise with both hands 10-15 times. You can easily perform this exercise 2-3 times daily.