In order to know where ordinares and charges, etc, are placed on the shield, you should know the terms of placement. There is no right and left in blazonry, instead they are replaced instead wth Dexter (Right) and Sinister (Left).

So you ask, why is the right handed dexter on the left side, and the left handed sinister on the right? Its a throwback to when heraldry was used primarily on actual shields, whether in battle or on the tournament field. The shield is to be viewed as if from the bearer of the shield, reversing the directions. Remembering the directions is fairly simple, most people are right handed, making them dexterous on the right hand side. Then think of holding the shield in your hand, and how the sides would be reversed by someone else viewing them. There is also a general rule of charges concerning this:

"Most heraldic charges, particularly animate ones, are drawn so they are facing dexter, as it is considered the more "worthy" side. So from the point of the viewer, rather than a bearer, any lions, for example, on the shield, would usually face the left-hand side of the shield."

The Complete Book of Heraldry by Stephen Slater

The shield is further divided. The top third of the shield called the chief and the bottom third called the base. These are both parts are further divided into thirds. Chief being divided into the dexter chief point, the middle chief point, sinister chief point, and the base being divided into the dexter base point, middle base point, and sinister base point.

The center of the shield is divided into thirds as well, but on a vertical axis, as opposed to the chief and base, which are divided on a horizontal axis. These subdivisions are the honor point, the fess or heart point and the nombril or navel point.

Use of these terms comes most into play when describing heraldry, which is called blazonry, in fact most of these don't come into play until describing the final parts of a armorial, and are for exact placement of charges or ordinaries.