What is the best black hair dye?

I got my hair professionally dyed black almost month ago, there's brown streaks throughout my hair underneath and my roots are starting to show. I'm sixteen and have never dyed my hair by myself at home but I wanna try it. What is the best brand of black hair dye in the boxes, not too expensive, easy and last long? please give me tips on how to do it and send me a link to you're question and i'll answer it.