(N.B. the opposite is ‘unroll’, not ‘roll down’)
Definition: to wrap something, such as paper or cloth, around itself several times so that it looks like a cylinder.
(This phrasal verb has more than one meaning)
E.g.1: He rolled up his newspaper and used it to kill the spider which was crawling up the wall.
E.g.2: If you roll the carpet up it will be easier to carry.
This phrasal verb can be separated. (E.g. 2)