These adjustable wooden hoops aren't just for embroidery. Embroidery hoops are essential for a variety of projects that require holding a piece of fabric taut and in place.
Embroidery hoops are an essential tool for inexpensive and easy screen printing at home. The hoop is used to hold a piece of mesh, drawn very tightly to create a screen. Negative (non-printing) areas of the image are covered with a waterproof latex paint. These screens are very durable, and will last for many many prints.
Darning is an old-fashioned method of repairing and decorating knit fabrics. Yarn is woven in a criss-cross fashion to create new fabric over holes, strengthen thinning fabric, and to make cool geometric designs.
The embroidery hoop is used to keep the fabric taut while you're working. Darning is easy, can save you some money, and it's a good introduction to working with embroidery hoops.