One of my problems is that I can't imagine things in my mind. I follow a audiobook of meditation and I must imagine / visualize a stairway but I can't do that. How can I fix or train it again that I can imagine that stairway and actually can see me of have the feeling that I'm moving down step by step at the stairway.

Even would this help to imagine that my legs are sandfilled sacks? I can't imagine that either. I hope someone can help me.