If you consider a sample of gas to be composed of a very large number of molecules running around in the container, you can start to understand this question. The molecule will travel in straight lines until they either 1) collide with other molecules or 2) collide with a wall.
Each time a molecule collides with the wall of the container, it exerts a force on the wall, pushing it back a little (if it is movable.) The more often molecules collide with the wall, the greater the total force is exerted against the wall per unit of area. (Force per unit area is the definition of pressure.)
There are three ways you can increase the pressure in the container.
1) If you increase the number of molecules in the container, there will be more collisions per unit area with the wall.
2) If you increase the temperature, the average speed at which the molecules travel will increase, and thus each collision with the wall will impart a greater force. This will also lead to an increased pressure.
3) If you decrease the volume of the container, the molecules don't have to travel as far to collide with the wall, so they will hit it more often. This will also lead to an increase in pressure.
So your question asks about an increase in volume. If you increase the volume, molecules have to travel farther to hit the wall and so they will do so less often. This should lead to a decrease in pressure.