Samahir, 

this distinction is significant in extremely limited situations when the grammatical or pronunciation rules vary with words starting with a vowel or consonant. 

There are very few French words in total that commence with ‘ y ‘ and apart from the difference in pronunciation of ‘ y ‘ itself, only a fraction of these require grammatical or pronunciation ( elision/liaison ) changes when the ‘ y ‘ is a vowel. There are so few words affected, and some are obscure technical words, that it is best simply to learn them if and when you encounter them. La Yougoslavie - feminine, consonant may be one you encounter sooner rather than later. 

At the start of a word :

if the y is followed by a consonant, it will act as a vowel. 

if the y is followed by a vowel, it will be a ‘ semi-vowel’ in French, that is it will act as a consonant.

 Only rarely is this important in regard to changing grammar or liasons.

 On its own, in the adverbial pronoun ‘y’, it is a vowel, but knowing that doesn’t really change anything. 

https://www.lawlessfrench.com/pronunciation/y/

 https://www.wordreference.com/fren/Yougoslavie