How does the tiny amount of air inside a container counter the great atmospheric pressure?

in text books the explanation given is that the air pressure inside and outside a container balance oit eacj other,but how can it be so?is not the atmospheric pressure too great compared to the pressure of the air inside the container?and i am uming that ofcourse the same atmospheric air cannot be acting from inside the container to counter the pressure from above,sure the atmospheric pressure can act on the sides of the container but cainly it cannot act inside out relative to the container?