Ok so, y = mx + c is the equation of a line
When a graph is written in this form, m is the slope/gradient and c is the y - intercept.
This form is needed when a question asks for the equation.
Lets say they give 2 sets of coordinates, we can use the point slope formula to find the slope (m)
point slope formula:
(y₂ - y₁) = m(x₂ - x₁)
Then we substitute any of the two set of coordinates to find c, the y - intercept.
So the line has a gradient of m and y - intercept of c