Chlorophyll is a wonderful molecule. It does not absorb light in the green spectrum so that's why leaves are green and it converts sunlight into 'plant food' and that's how plants live (the process is a bit more involved than that).
In deciduous plants leaves turn from green to yellow (or red, orange, purple..) then fall off. Leaves eventually decompose and form part of the organic layer of surrounding soils.
Next Spring new leaves filled with chlorophyll will appear and the process will be repeated.
