Field
The field is the background of a shield, the surface every other part of the arms sits on. It can be a single tincture, divided into two or more parts, or covered with a repeating pattern such as stripes or checks. A blazon always describes the field first.
A plain field is the simplest kind, as in Austria's red shield with its white fess. A divided field splits the surface along a line: per pale is down the middle, per fess across it, and quarterly makes four parts. Patterns like barry, paly and chequy repeat a division over and over. Whatever sits on top of the field is a charge.
The Shield tab of the coat of arms maker sets the field. Choose Plain field or a division such as Per bend, Per chevron or Tierced in pale, then click each part to give it a tincture. The heraldic divisions guide shows every option with its proper name.