Ok, I think you mean:
y = mx+c
and its simple.
1. This equation is a straight line equation (so if you are asked to draw that you know it will be a straight line)
2. the m stands for the gradient which just means how "steep" the line is. this can be found by doing y2-y1/x2-x1
3. The c is the y-axis intercept is where the line crosses the y-axis (so you just look at the graph and look for the point where the line crosses the y-axis)
If you are given a straight line and is asked to give its equation then you know that it will be y=mx+c
then you find the value for m by doing y2-y1/x2-x1
the y's and x's here are found by taking any two points from the graph and looking at the "co-ordinates" this means you look for where on the y-axis the point is and where on the x-axis the point is and then just substitute that into the equation to find m.
to find c you just look at where the line crosses the y-axis..
