A simple way to represent a function is by drawing its graph. For each input $\Tblue{x}$ on the horizontal axis, called the $x$-axis, we plot the corresponding output $\Torange{y}=f(x)$ are on the vertical axis, called the $y$-axis.
The graph of a function gives its value for each possible input. Here, $f(\Tblue{2}) = \Torange{4}$
The function $\Torange{y} = 2 \Tblue{x} -3$ and its graph