Sorry, that was mean.
Here's a better way to say that.
You know, the difference between "a" and, "an" may surprise you (totally legit no cap definitely). When saying "a" as in "a bird", it always goes before words that start with a consonant such as "gorilla"; "an" on the other hand goes before words that start with a vowel such as "apple". When saying a number, you would mostly base "an" and "a" off of what it sounds like, rather than its spelling; for example "one hundred" would sound like "won hundred" so you would say "a one hundred-"; when saying, "eight" it still has the vowel (e) so you would say "an". You wouldn't tend to use "a" and "an" before numbers because it's not grammatically correct to say "a one person" you would just say "one person" but when talking about the thing about "person", you would say "a one person event" for example.