Continuous variables can have values (called a quantity) that can be given a magnitude (size) either by counting (as in the case of the number of shrimp) or by measurement (e.g. light intensity, flow rate etc).
For example: If you investigate the effect on the resistance of changing the length of a wire, the length of a wire you are using is a continuous variable since it could have any length you choose.
e.g. Carol is interested in the force between magnets. She fixes one to a top-pan balance and clamps another directly above it.
By varying their separation, she can investigate the force of repulsion. The separation can have any value at all, so we call it a continuous variable. Line graphs enable you to show this type of variable very well.