A buttonhook is a tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 used to facilitate the closing of shoes, gloves or other apparel that uses buttons as fasteners.

It consists of a steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 hook fixed to a handle which may be simple or decorative as part of a dresser set or chatelaine

Chatelaine (chain)

Chatelaine is a decorative belt hook or clasp worn at the waist with a series of chains suspended from it. Each chain is mounted with a useful household appendage such as scissors, thimble, watch, key, vinaigrette, household seal, etc....

. Sometimes they were given away as promotions with product advertising

Advertising

Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...

on the handle.

To use, the hook end is inserted through the buttonhole to capture the button by the shank and draw it through the opening.