Textured rollers are rolling pins, made out of wood, rubber or plastic, with a pattern carved into the surface of the roller. These are then usually rolled over soft leather hard clay. 

As they are rolled across the clay, they leave the texture of the design behind them on the clay surface.

Clay Texture Rollers – View on Blick

Some potters will use a roller directly on a freshly thrown pot, to get a maximum impression of the design on their ware. 

But when pottery is freshly thrown, it is very soft and loses its shape easily.  So, after the texture is added, some work has to be done to restore the pot to its thrown symmetry.   

Alternatively, you can use textured rollers as a way of decorating pottery when you are hand building.  ThePotteryWheel suggested as one of the best ways to use a textured roller is when you are slab building. 

You can either use the roller once the piece has been formed.  Or, you can add the texture to your unformed slab and then shape it carefully into whatever form you choose to make. 

Reference -  thepotterywheel.com -