Khan Academy
The following link goes to a section of the Khan Academy website devoted to linear graphs. There is a prolific number of videos dealing with various aspects of linear graphs. Also, if you click on the Practice Concept tab in the top right corner of each topic, you have the opportunity to solve practice problems. 

https://www.khanacademy.org/math/algebra/linear-equations-and-inequalitie

Here is the link to an excellent website which has many pages,with applets, relating to linear graphs. This link goes directly to a page explaining gradient. 

http://www.mathwarehouse.com/algebra/linear_equation/slope-of-a-line.php

Yay Math
The video below from Yay Math shows that very cool dude explaining gradient or slope.

Go via this link to MyMathsOnline and view a lesson about gradient and how to use the Gradient Formula

http://www.mymathsonline.com.au/tasks/library/loadLesson.asp?title=graphs/graphs2Gradient&taskID=1312

Go to this link to review how to find the equation of a linear graph from two points on the line. There are some practice questions as well. 

http://www.mathwarehouse.com/algebra/linear_equation/write-equation/equation-of-line-given-two-points.php#examplePointSlope

Here is an applet which demonstrates all the different forms that a linear equation can be written in. Drag the red dots to change the position and equation of the line.

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Slope Interept Form Point Slope Form Standard Form

Toggle Points Slope? Show Rise and Run ?

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More Math Applets by www.mathwarehouse.com