A teaching coat, not a grant. Choose a field, an ordinary and a charge. The plaque writes the blazon in the old word-order: metal or colour first, then the ordinary, then what stands upon it. Rule of tincture: metal should not lie on metal, nor colour on colour.
Grammar follows English blazon as taught in Fox-Davies and the College of Arms primers: field, ordinary, charge; “a” not “one”; animals default rampant unless said otherwise. This workshop is a didactic shield — it does not search the official registers, and it will not tell you whether a coat is already borne.