Vertical and Horizontal lines: 'x=a' and 'y=a'
x=a is a vertical line through 'a' on the x-axis
y=a is a horizontal line through 'a' on the y-axis

Other Lines Through the Origin: 'y=ax' an 'y=-ax'
y=ax and y=-ax are the equations for a sloping line through the origin.
The value of 'a' (known as the gradient) tells you the steepness of the line. The bigger the 'a' is, the steeper the slope. A minus sign tells you the slope is downhill

Straight lines:
x - y = 0
y = 2 + 3x
2y - 4x = 7
4x - 3 = 5y

You might be asked to draw the graph of an equation in the exam.
1) Choose 3 values of x and draw a table
2) Work out the corresponding y-values
3) Plot the coordinates, and draw the line

2) Find the y-values by putting each x-value into the equation
When x = 0,
y = 2x -3 = (2x0) - 3 = -3
y = -3
When x = 4
y = 2x -3 = (2x4) -3 = 5