The liquid particles in a container are at rest. There are a lot of forces from all sides on a liquid particle at any depth, except on the surface. The liquid particles are at rest in equilibrium as the pressure from all sides keeps them at rest.
The liquid particles are like a jam packed bus, and totally packed local train. There every one is stationary, as no where to move. But every one is exerting pressure on another laterally. The persons at the walls are pushed against the walls. The exert force on wall. Wall exerts pressure on them equally. That force is cancelled by the people behind him.
The people standing at the door only face forces from inside. Like the particles at the surface of a liquid.