I keep meaning to write a program that will do a better job of graphing this than the one I have (Training Peaks WKO+) but for now it'll have to do (because beer and lazy)
It took me a while of staring at this to understand it myself so I'll try to explain best as I can.
Each bar represents 4 weeks. The height of the bar is the peak power output you sustained during that 4 week period. There are 4 seperate graphs in this window, each of which is for a different length of time.
Take the set on the far right for example, there are 5 bars there increasing in height. The whole set is a graph of how much power I can sustain for 20 minutes at a time. Each bar represents the best 20 minutes I did in that 4 week period. Does that make sense?
The bars on the far left graph look weird because many of them are *too low to be on the graph*. Partly this is because this is my weak point, and partly because for the periods shown here, I did not do a lot of peak-power training. The two sets of graphs on the right show the most steady improvement (the blip on the 5-minute graph is basically that all I did during that period was long slow steady rides). I'm pretty happy that the graph goes up - that's about all I care about.
The massive beat is that I have this selected as "female" because otherwise a lot of the bars don't show. However - the graph for "male" says that my 20 minute power is within sort of standard "cat 5 range" and my 5 minute is nearly so. I don't think 5s shows up at ALL on that graph.