Adrian Underhill, in his book Sound Foundation, defines consonants as follows: “Consonant sounds are made by restricting or blocking the airflow in some physical way, and this restriction, or release of the restriction, is what gives the consonant its characteristic sound. By contrast, vowels require the vocal tract to be open so that the air stream escapes unobstructed.”

The English language has 24 consonant sounds. The two main characteristics to look for in a consonant sound are whether it’s voiced or not and its manner of articulation. Determining whether a sound is voiced or unvoiced depends on whether it vibrates the vocal cords it not. To decide on the latter, the sound’s manner of articulation, is by examining how the sound is produced. 

Some technical terms that may be of importance to those of you studying phonology. 

The unvoiced sounds take energy to utter so they are called fortis, whereas voiced sounds are gentle and do not require as much energy, so they are called lenis.

+ voiced and lenis                    -unvoiced and fortis