A molecule can be represented in a couple of different ways. 1
The detail is given below:
# Chemical Formula
In this way, each of the atom of the molecule is counted, and the number is shown in the subscript. For example: $C_4H_9OH$ is the chemical formula of Butane.
# Full Structure
Using this representation, all of the atoms and their bonds are shown. For example, the above mentioned butane would be represented as:
Each dash represents a covalent bond.
# Line-angle Structure
This is a more compact representation, where C is assumed at the corners or ends that don’t have any explicit atom shown, and hydrogen is assumed based on the carbon valency and free bonds.