Short answers, pulled from the story.
Composition in visual arts is the organization of an artwork, derived from the Latin meaning "putting together." It involves the deliberate placement and arrangement of visual elements including line, shape, color, texture, value, form, and space. It is distinct from the subject matter of a work.
The rule of thirds is a composition guide that places important features of an image near the horizontal and vertical lines that divide the picture into thirds, ideally near their intersections. It is considered a simplification of the golden ratio, though there is little historical evidence that artists widely used the golden ratio itself.
The rule of odds states that an odd number of subjects in an image is more interesting than an even number. An even number of subjects tends to create symmetries that can appear less natural in informal compositions. Three subjects are suggested when more than one is shown.
Color has three properties in visual art: hue, brightness or chroma, and value. Chroma measures the purity and intensity of a color; value measures its lightness or darkness. Color can also be used to create mood, tone, pattern, movement, symbol, form, harmony, and contrast within a composition.
Positive space is the subject of a piece, while negative space is the empty area around, above, and within the subject. Both are recognized elements of design used across photography, painting, architecture, and drawing.
Paul Cezanne successfully used triangles in his compositions of still lifes. A triangular format creates a sense of stability and strength within an image, and triangles are considered an aesthetically pleasing implied shape in visual composition.