A syllable can be made up of just a vowel — "a" can be a syllable — or a vowel and one or more consonants — "skip" is one syllable, but three sounds, or phonemes: sk-i-p.
When you're figuring out how many syllables a word has, you have to listen to how it's pronounced, not look at the spelling. Household is two syllables — which you'll hear when you say the word — even though it's got four vowels. Elephant is three syllables, and hippopotamus is five. You can also use syllable for the tiniest bits of language: "I loved every syllable of your speech," or "Please don't repeat a syllable of what I told you."