In terms of consonants and vowels, the following words represent the following structures:
One fact that one may notice from these structures is that they all contain a vowel. This vowel is known as the nucleus of the syllable.
Another fact is that a syllable may have a consonant or string of consonants before the vowel. These consonants that are before the vowel are called onsets.
Finally, a syllable may have a consonant or string of consonants after the vowel. These consonants that are after the vowel are called codas.
The following diagram is an illustration of a syllable such as the one in cat:

In the next section, there will be a discussion on syllabification.