The main idea behind finding the equation of a straight line is centered around finding the gradient and y-intercept.
We have to remember the concept of a gradient is found by finding the change in y divided by the change in x. Its a rate of change of the y values wrt the x values. Some use the method of rise over run too or rise/run. Keep in mind that checking that your answers are correct, especially knowing that when a graph slope right it is positive, and the left will be negative.
The word intercept means to cut/meet at a point. So y-intercepts meet at the y-axis/cut the y-axis. This is drawn straight from a straight line equation (look for the term without "x" or the constant/number).