I'm not super big on mascara, because my lashes are already dark..so I usually apply clear mascara (yes, clear..LOL) and then use the curler. If you were to use it w/ black mascara, I suppose you could do it either way, before or after, after might get some mascara on the wand, but I don't think it would be too hard to clean off.
It does curl the lashes--you start at the base of the lash and brush upward, kind of curl your wrist..when you get to the end of the lashes you can hold it in place for a couple seconds which helps them stay curled upward.