Maish, try to reach the plate, as soon as your at it you need to hit triangle.. eer, dunno what that will be on the box, probably Y. With the green you will run fast towards another plate (or platform), when you reach the new plate you just need to hit Y again before you fall, to continue running.
The yellow plates will make you fly and the red and blue ones got some weird flying as well, but at least here you don't haveta watch out for obstacles.
As you unlock plates you can go back to previous levels to reach more energy bubble thingys. You'll see some levels got the red or blue, etc plates even though you don't need them to reach the fertile grounds.