A rasp looks like a file but instead of having long teeth the theeth are brought to points. The come in a varity of shapes and tooth patterns. For the smoothest finish use rasps that have been cut by hand to a random tooth pattern. They come in a varity of shapes and teeth patterns. A inexpensive general porpous rasp is called a 4 in 1 rasp and has four tooth patterns on one rasp.
Rifflers are related to rasps however a riffler has the cutting surface bent to lift the handle out of the work area. Rifflers are used for cutting shallow depressions.
Rasps and rifflers should only be used on soft materials like wood, soapstone etc. Metal will dull them quickly. They can be sharpened many times in an acid bath.