Molecules that have charged parts to them are attracted to the charges within the water molecule. This is an important reason why water is such a good solvent. So for instance the picture below shows a glucose molecule in solution. Water molecules surrounding the glucose molecule are shown in blue for clarity.
Glucose molecules have polar hydroxyl(OH) groups in them and these attract the water to them. When sugar is in a crystal the molecules are attracted to the water and go into solution. Once in solution the molecules stay in solution at least in part because they become surrounded by water molecules. This layer of water molecules surrounding another molecule is called a hydration shell.
