You have many options.
1) Take a photo and load it on your computer. When posting to this forum there will be a little icon with a picture of a photo. You can click that and upload your photo from that tool.
2) Use an art program like Microsoft Paint to illustrate your problem and work and upload it as above.
3) You can use a formatting language called Latex which produces an image for you, but there is a learning curve to this (quote my post to see how the image is created): \(\displaystyle f(x) = 2x^3+\dfrac{1}{x}\)
But if you mean a kind of "white-board" instant post feature, that is not available on this website, but it is a great idea.
