How might a theory relate to a model in science?

A model is a structure that makes all sentences of a theory true. A theory is taken to be a set of sentences in a formal language. the structure is a model in the sense that it is what the theory represents.
Example: 'any two points can be joined by a straight line'

Any structure where all these statements are true is a model of Euclidean geometry

answer and explanation;

composition refers to both the types of minerals within a rock and the overall chemical makeup of the rock while texture refers to the size and arrangement of the minerals or grains that make up a rock. both composition and texture can be used to classify rocks, such as igneous rocks. texture describes how the rock became solid or crystallized from liquid, melted rock. composition of a rock describes the minerals that make up a particular rock.

The radiation of the fire causes the saucepan to heat up. the conduction of the saucepan then to distribute the heat over the saucepan and to give heat to the water. the convection of the water distributing the heat within the water, till all the water is boiling