Potato ricers are like big garlic presses (or maybe it’s that garlic presses are like small potato ricers). There is a chamber usually large enough to hold one or two small boiled potatoes and, using levering action, the attached plunger squeezes the potato through small holes in the bottom of the chamber. It is called a ricer because the potatoes that are forced through resembles rice.
Most potato ricers have interchangeable plates with different size holes. If yours does, make sure that you disassemble and clean them as soon after use as possible. Dried potato starch is much like glue and getting it apart later will be difficult.
The ricer that my mom had when I was growing up was made from cast aluminum but you can find chromed steel or stainless steel on the market as well. I have one that is made of plastic that I especially like. It came with three discs.