Repair, alter, or create clothing.
Upholsterers work with the fabric and seating components of furniture. An Upholsterer can work on a plane, a train, an automobile, or really anything that has fabric and seating. So mostly chairs.
In a piece of furniture there are generally four components: The frame, or underlying structure of the piece (usually wood), the spring system, which provides a firmness or softness, the cushioning or padding, and the fabric covering. It is your job as an Upholsterer to build or rebuild the latter three components— everything from the frame up. This requires a vast knowledge bank of woods, fabrics, textures, cushion fills and springs, so when a costumer comes in you can communicate to them the color, textural, and tactile possibilities their furniture holds.
This position is mix of engineering and design. At its core, furniture is defined by its structure, and thus its beauty arises from that structure. Through upholstery you can retain and enhance the structural beauty with different fabrics and springs to add comfort and aesthetic appeal.
To do this you need strong sewing skills, a good ability to match colors and textures, and a sharp eye for detail. Your daily tasks might involve patching up holes where stuffing is trying to escape, and evaluating the structural integrity of a piece by examining the frame and joint structure. On the whole you understand how to make a seat mold nicely to your beautiful seat, and are able to explain, implement, or repair any elements that prevent it from doing so.