Plug in x = 0
f(x) = 4x-2
f(0) = 4(0)-2
f(0) = 0-2
f(0) = -2
The input x = 0 leads to the output y = f(x) = -2
The point (x,y) = (0,-2) is on this line. This is the y intercept where the line crosses the y axis.
If you plugged in x = 1 then it would lead to y = f(x) = 2. I'll skip the steps since they are similar to what is shown above.
Plot the two points (0,-2) and (1,2) on the xy grid. Then draw a straight line through them to complete the graph of f(x) = 4x-2.
The graph is shown below.