These sound like topics that would make for some good tutorials.
Long answers, so I spoilerized them to shorten this post up. Also, these answers are fairly general in the way I explain things, so if you need more detailed info, don't hesitate to ask!
1) I don't know why my texture paint is not working. Each time I try paint using texture paint, it won't work, so I will how have to use vertex paint.
2) Why is it that when I want to paint and put it on vertex paint, the model turns white like paper and I have to use all four views guessing to paint then later check what am painting with texture paint.
3) what is the use of vertex paint?
4) What is the use of weight paint? Each time I select weight paint and select a particular color, and then start painting, it paints with different color I don't know why.
Hopefully that clears some things up! If you need me to clarify anything, feel free to ask!