there are a few different types, some are a touch up pen, but then the whole top twists off to reveal a touchup brush too, the brush is better than the pen, the key is to wipe the brush just about dry so you don't blob on too much, you can always add or go over it if you need too. some types also come with a color & a seperate clearcoat, don't think nissan uses those though...
remember, a touch up is never going to be invisable, but if it makes the blemish the same color & fills it in somewhat then it can hide it fairly well. good idea to have a little laquer thinner handy if you make a mistake just wipe it off & try again, also you should clean the chip(s) out well with laquer thinner too before the touchup, laquer thinner won't hurt you paint but be careful with it on lenses & other plastic trim...