"es" and "as"?

I've been learning Spanish for about 4 years now mostly Colombian Spanish if it makes a difference in this context. Anyway my question is when can you use "as" and " es" at the end of a verb? Example: no olvid(es) o no olvid(as) Is it truly interchangeable in all situations? When are they used and is there a reason? I still don't understand lolol I see people use both seemingly interchangeably. I don't know many grammatical terms even in my first language so I apologize if my wording is confusing.

submitted by /u/domecycleripworm
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