This type of footstool is used to provide comfort to a person seated, for example, in a chair or sofa. It is typically a short, wide, four-legged stool with a padded top, upholstered in a fabric or animal hide, such as leather. This type of footstool is also a type of Ottoman and it often referred to simply as an Ottoman. It allows the seated person to rest their feet upon it, supporting their legs at a mostly horizontal level, thus giving rise to use of the term footrest, for this item.
This type of footstool, also known simply as a stool, is used as a short stepladder or to support a person's (usually a child's) feet that do not reach the floor when seated. In the former case, the footstool is used by placing it on a flat surface and standing on it to extend one's reach. In the latter case, the footstool is placed under the feet of a sitting person so that the person's feet may rest comfortably on it. An example of the latter is the type of piano footstool used in conjunction with a piano bench.It is also used to make the blood circulation of your body flow more freely than sitting down.
Generally, any object of suitable elevation may be employed as a makeshift footrest. Another seat, a desk, or a table may serve. These options are usually considered inconsiderate since feet, and especially shoes (by their nature) tend to collect more dirt than a person's working area or pants.