Consonants and Vowels

What's the difference between a consonant and a vowel?

In grade school, I'm pretty sure you've been taught that there are 5 vowels: AEIOU. The rest are consonants. However, this distinction fails to take into account the sounds of the letters. There are more sounds in English than there are letters (in the written form). The sounds and letters of a particular language do not always form a 1 to 1 correspondence, and this is why we must use 2 letters to represent a single sound (such as "sh").

How we produce speech sounds

The process in which we produce sound by using our vocal tract is much like that of a wind instrument. Each sound differs from another sound by a unique combination of features: the way you shape your mouth and tongue and move parts of the vocal apparatus when you make the sound. Air coming from the lungs passes through the vocal tract, which shapes it into different sounds. Then the air exits the vocal tract through the mouth and/or nose.

What differentiates a consonant and a vowel in terms of speech sounds?

Quite simply: Consonants are pronounced by obstructing the airflow through the vocal tract.

(Note: the details of how to pronounce every sound is beyond the scope of this site)

Example:
The [p] sound is made by obstructing air at the lips. When you say the word put, air is built up behind the lips and then released.

On the other hand, vowels are different from consonant sounds in that they are produced by passing air through different shapes of the mouth and different positions of the tongue and lips.

Examples:
For the "ahhh" sound (the vowel in the word pot, IPA [ɑ]) the tongue's position is in the lower back of the mouth.
For the "eeeee" sound (the vowel in the word be, IPA [i]) the tongue's position is in the upper front of the mouth. (This is why we say cheese when we take pictures!)