first of all I would like to warn you, if that is you in your picture, your hair will most certainly not go blonde from bleaching it. It would probably take several attempts, of which will ruin your hair, trust me I know. But I also know that people told me that when I wanted blonde hair and I didnt listen and you probably wont either. LOL my suggestion to you is that you go to a hairdresser and tell them the color you want your hair. It will cost more than a box of bleach but the results will be worth it. And your hair will thank you.
The devellopment cap IS the cap that you pull the strands through. you will need a shit ton of bleach to bleach hair evenly doing a whole head. and OMG your hair will feel like straw after. the only thing that fixes it is cutting it off. Trust me, I know. my profile picture is me, after my haircut of 9 inches to get as much of the bleached hair out as possible. and though it looks nice in the picture, it felt like shit and I still have about 4 inches of bleached hair on my head that feels horrible.
Once you bleach the crap out of your hair, it will be a orangy or yellowy color (if you are lucky) to get rid of the yellow/orange, you need a toner. these are normally only sold in salon service stores. After you use the toner, you need a blonde dye. You know, a box of dye from the drugstore that the lucky people who already have blonde hair can buy and just put on their hair... yea that one. that way your hair doesnt just look like.. well.. trashy bleach blond 1980 Courtney Love hair (unless ofcourse thats what you are looking for!, in which case, disregard all of the above and go hard! )
Best of Luck to you!! xx