This is the way I prefer to bleach and color the tips/ends of hair. I have done this method to my own hair and the way I do it for multiple others.
First off though I would like to suggest that you do deep condition or prep your hair before you bleach your hair even if it is only the tips. I have seen so many others think if only a section or the ends that it will not matter, but honestly if not properly prepared it can damage your hair. I personally do a good deep conditioning before.
So you will of course need to go buy your bleach and developer. Make sure you follow the instructions exactly when mixing. As far as which volume you should use, that will depend how dark your hair is and how many levels do you want to lighten the hair. So if you do volume 20 for example, it will only maybe lighten your hair by like 1 or 2 levels lighter, but volume 40 will significantly lighten your hair.
So once you have your bleach and developer properly mixed, section off your hair into small 1 or 2 inch segments, not as bad as it seems plus you will have a much cleaner look and less chances of having spotchy areas. You will also need a hair dye brush, or you can use other things, such is eyebrow brushes, etc.. you can even use fingers if ultimately have to but make sure you are wearing good gloves. I will recommend highly though to use some sort of small brush or comb.
Now take each of the sections one at a time and brush the bleach/developer on the ends of your hair, which the width of the ends bleached is your personal preference, I will suggest brushing the bleach from the higher point of where you want it bleached to the ends and not from ends to the top point.
You can use either an aluminum foil or even a sturdy plastic wrap to keep each of the sections from touching anything or even mixing in wrong with other part of your hair. Keep the bleach in for as long as the brand you buy recommends.
I then individually unwrap each section and thoroughly rinsing the individual sections, again keep the other sections wrapped until it is their turn in the water.
You can then dry and style as you wish.
I really hope this helps even if only a little.