Solar Energy

i wan to ask about solar energy because i know nothing about solar energy. how actually solar energy work?and how many type of solar energy?i buy a solar energy torchlight from china,why it duration of energy so short?after i charge for it in the day time,then if i dont use it,the solar energy gone and the energy like cant save in the device,i wan to ask whether is the quality problem?and there is solar energy device which can save the energy for long duration?what is the watt,voltage or resistance in solar energy normally?which combination is the best?i mean watt+voltage+resistance. i wan to know everything about solar energy.please