To discuss the shapes and components of molecular structures, we need an easy way to draw the substances. One example is the ball and stick diagram.
In these diagrams the ‘balls’ represent atoms. If your substance is a compound then it will have multiple different types of atoms. Different atoms can be distinguished with different sizes, colors, and/ or labels.
The ‘sticks’ are covalent bonds which hold the atoms together. The length of these bonds and the size of the atoms are not to scale in these diagrams as the goal is only to convey the structure and composition of the substance.
To better convey three dimensional structure, bonds can be drawn as thicker or dashed to represent a bond coming ‘out of the page’ and ‘into the page’ respectively.
Figure 1 - A ball and stick diagram of ethene