Brushes

Brushes for watercolor are made to hold water and are softer as compared to the stiffer brushes used for acrylic and oil paint.
Watercolor brushes come in various shapes including flat, round, mop, and fan. There are numerous specialty brushes; for example, a long thin brush originally designed to paint the lines of rope (rigging) on a seascape is called a "rigger".
Artists typically have a few favorites and do most work with just one or two brushes. A single brush can produce many lines and shapes. A "round" for example, can create thin and thick lines, wide or narrow strips, curves, and other painted effects. A flat brush when used on end can produce thin lines or dashes in addition to the wide swath typical with these brushes.
Brush hairs come from a variety of sources including the very expensive hair of the Kolinsky Sable, the ear hair of the ox or other cattle, and others. "Camel" is used to describe hairs from several sources, none of which is from a camel.
Brush hairs can be natural, synthetic, or a combination. Brush prices vary considerably depending on the type of hair and the quality of the manufacture. A good brush will hold a fair amount of water and will keep and return to its original shape even after much use.
Brushes are numbered to indicate the size of the brush, the larger numbers for the larger brushes. A typical manufacturer's offering of brushes might go from a very small "0" to the larger size "20" or more. Flat, wide brushes are usually described by the width of the brush such as "1/2 inch" or "1 inch". There are no common standards for brush sizes. A "10" Round from two manufacturers might be slightly different in size.