When we talk, our mouth makes lots of different sounds. These sounds are called "letters" and they help us make words. Sometimes when we talk, we make sounds that are louder and more forceful than the other sounds. These sounds are called consonants.
To understand what a consonant is, think of the word "cat." When you say "caaaaat," you can feel your mouth open wide for the "a" sound. But when you say the "c" sound at the beginning of "cat," your mouth closes up quickly and the sound is more forceful than the "a" sound. That's a consonant!
Consonants are important because they help to distinguish one word from another. For example, if we didn't have the "p" sound in "people," it would sound like "eeple." So, we need consonants to make clear, distinct sounds in our words.