Osmotic pressure is basically the pressure that you need to exert on a semi permeable to keep the solution contained on the other side. It is a representation of the number of solute particles in solution. The relation between both is that the greater the number of solute particles contained in the solution, the greater the osmotic pressure.
In effect, the osmotic pressure is ultimately exerting an influence on the other solution. The solutes can be small electrolytes or it can be protein molecules. Each solute exerts a specific amount of osmotic pressure, depending on its weight or the number of molecules.