Stumps are tightly rolled paper "sticks" that can be used to blend lines or areas of pencil (graphite) or charcoal.  You get them from an art supply store.  They come in different sizes from fairly small to larger.


You can use the stump to smear or even out the graphite or charcoal on your paper.  It can be more precise than your fingers and it carries no moisture or oil as your fingers might.


Keep your graphite stumps separate from the ones that you use for charcoal to keep the two mediums separate (if you wish).  Stumps can be cleaned by rubbing them on a clean piece of paper to rub off the medium (charcoal or graphite).  They can also be cleaned by rubbing them with a kneaded eraser or by rubbing them on sand paper or an emery board.  


They can be reshaped and re-sharpened by sanding them on sand paper.  I have also clipped them with scissors.  A knife or single edge razor blade might work too.  You can follow any major shaping by a refined shaping with the sand paper. 


If you don't have a stump you can wrap paper or paper towels around a sharp pencil or smaller stick and fashion something similar.  It is possible to draw by just using the pencils themselves or the charcoal or skipping blending with another tool altogether.