The chart tool is set up so you can see each major currency pair and how it compares to all other pair on each time frame.
The green blocks indicate that that currency is very strong on those particular times frames then any other currency.
On the contrary, the red blocks indicate that the pair is weaker then any other currency on that particular time frame.
In the example image above, you see that the pound sterling is very weak indicated by the overall average as dark red box.
So we can conclude that right now EUR is the strongest, whereas, GBP is the weakest.
How easy was that??
So how can you profit from strong and weak currencies?
Well, using another illustration, have you ever arm wrestled someone before?
Take a look at this image: