Correct sentences:
- There are three buffaloes, and they have six horns.
- The three buffaloes have six horns.
- Three buffalo have six horns. (You can also say "buffalo" as the plural.)
Why these are correct (easy steps):
- "Three buffaloes" is more than one, so we must use are (not is).
- For more than one animal we use the pronoun they, not it.
- Both "buffaloes" and "buffalo" can be used as the plural form.
Quick tip: If you are talking about more than one thing, use "are" and "they."