The independent variable almost always goes on the x-axis. This leaves the dependent variable on the y-axis.
The independent variable is one that is not affected by the other, while the dependent variable will vary depending on the independent variable. Typically, the independent variable is specified, while the result that is measured is the dependent variable.
The independent and dependent variables can be related to the cause and effect during an experiment. The size, position or speed of the independent variable is the cause that will influence an effect, which is the dependent variable you are measuring. Any property of either variable can be tracked and plotted against each other, even if they are different from each other. Once a graph is constructed, it will be clear how much, and if, the independent variable influences the other.
Not all equations and graphs are two-dimensional. In an experiment with two independent variables, which are usually designated as x and y, the dependent variable is usually z. The z-axis is the third dimension that typically represents depth or height. It is possible to graph a three dimensional representation of the results, but it is also possible to plot two separate two dimension graphs. This would be done by first plotting the z-axis vertically and the x-axis horizontally, and then plotting the z-axis vertically but the y-axis horizontally.