If you make it with water, you will get a hot chocolate with a more intense cocoa flavour. If you make it with milk, you will get a chocolate with a smoother taste.
If you add more water or milk, you will get a more liquid chocolate. If you add more chocolate, the chocolate will be thicker.
If you want to make a quick hot chocolate, we have good news for you: you can also make it in the microwave! Heat a cup with 100ml of water or milk, melt the chocolate and stir. Heat again until it boils and the chocolate rises. Remove the cup and repeat the process until you get the texture you want.