If you want to lighten your hair its called highlighting. I would suggest going to a salon to have it professsionally done they will know what to use to lift your natural color. Sometimes the products purchased in the stores is not strong enough to lift darker colored hair, in which case it will cause hair to turn orange.
That depends on how dark your hair is in the first place. If it's black or dark brown I HIGHLY suggest you get a professional to do it. A quarter cup of bleach to a gallon of water sometimes works but it can turn some hair orange.
You can buy bleach kits at many department or drug stores. The best way to get lighter hair is go go to a professional salon where they are specifically trained to do services like this.
People i know that have lightened their hair have used bleach. A few of them went to the salion to have them do it. But you can do it at home. Just take bleach and apply it to your hair,then dye your hair the color you want it. If you want light hightlights then only apply it to strands.
I use a bleach, usually a powder I mix the powder bleach with the creme developer
and leave on for 20 minutes, you should check it to make certain it's light enough, then
rinse it out, dry it, and add your blond color over the top of it. Then just leave the blond color on for 25-30 minutes, and rinse.