A/anis usually followed by

'A' followed by the next word which uses consonant as the first letter. Ex: A sofa; a cat; etc.
'An' followed by the next word which uses vowel as the first letter. Ex: An alligator; an animal; etc.

[Exceptions]
For 'university', 'universe', or others which are pronounced as 'yu' as the first letter, they need to be started with 'a', not 'an'.


Semoga membantu yaa, maaf kalau bukan begini yang dimaksud ^-^