(Non-expert-question) What exactly do chloroplasts do when they "convert light into chemical energy"?
I see you've given this a try, so here's a synopsis hopefully appropriate to both your current knowledge level and curiosity.

Light excites electrons in chlorophyll to a higher energy. Higher energy means less stable, those electrons want to return to a state of lower energy. The chloroplast is structured in such a way that the electrons, instead of just plopping back to the lower energy state in the chlorophyll to liberate the light they just absorbed, are handed off to another molecule. As the electrons get passed off to other molecules, they lose energy. All of this is taking place on a membrane within the chloroplast. The energy being "lost" by the electrons is harnesed to pump hydrogen ions across that "thylakoid" membrane in the cholorplast. The increased concentration of H+ within the thylakoid space is another form of energy that can do work. The work done is the creation of ATP.

We're not done with those electrons yet. They get passed off to yet more molecules, losing energy again in each hand-off. This energy is used to create additional energy-rich substances that will power the creation of energy-rich organic molecules in a process termed the Calvin Cycle. The Calvin Cycle, which creates the sugar G3P from inorganic CO2 from the atmosphere, also takes place within the chloroplast.

So, the chloroplast is a multi-talented factory for the conversion of CO2 into sugars. These sugars provide both energy and carbon, in a useable organic form, for other processes in the plant. Chloroplasts also contain DNA. This, and other evidence, suggests that chloroplasts, like mitochcondria, were once free living organisms that got co-opted by other organisms and now exist within cells in a mutualistic association (the Endosymbiont Theory).