* The "y" in "by" is a consonant. It makes a "y" sound, like the beginning of "yellow".
* Vowels are the sounds you make with your mouth open. Think of "a, e, i, o, u".
* Sometimes "y" acts as a vowel at the end of a word, like in "happy" or "fly".
So, in the word "by", the "y" is a consonant.