J is for Jelly Roll
You can also buy a pack called a charm pack which works in the same way as a Jelly roll pack but the quilting materials in those packs are 5 inch square pieces.
Jelly rolls are popular as the measurements are a pre-measured consistent size internationally so it makes it easy to mix and match from different shops sticking to your own colour scheme but keeping and buying the same measurements each time.
Jelly rolls are used for a very wide variety of things, people make patchwork quilts, smaller items like pin cushions some people just buy them as they use such small amounts of materials in their handmade goods they come in handy for a wide variety of uses.
2. If you want to wash your material before using it use small amount of washing powder in a bowl in luke warm water. Swish around the fabric gently using hands (would recommend wearing some plastic gloves) or small wooden spoon. Allow fabrics to soak for around 15 minutes and then drain out and wash again under running cold water to rinse washing powder out of materials. Squeeze out excess water and then allow to dry and iron flat again before use.
There are several sites which provide free Jelly roll patterns to help you decide what to make with your jelly roll including: