In my science book it is written that as the pressure increases the melting point of a solid decreases but i think that it is wrong as the pessure will make the molecules stick together instead of flowing like liquid thus increasing the melting point right? So my book is wrong right?
First of all, it's not universally true. Particularly with solid phases that only appear at high pressures.
But the reason why it does often occur, e.g. with ice, is that as you increase the pressure, you force the atoms closer together which causes the enthalpy of the system to increase. Increasing the pressure of a liquid phase, on the other hand, does not produce the same enthalpy rise. This is hopefully intuitive: since the atoms are not rigid, they are better able to respond to pressure-induced changes in the local structure.
Consequently, the free energy of the solid phase increases more than the liquid phase, which shifts the transition point (where the free energies are equal) towards the solid phase.