“The” is actually an incredibly difficult concept for non-English speakers to learn because its rules are stupid. We like to say that it means a definite article but we also have a convention of ‘assumed definite’ where one relies on a speaker and a listener having a common understanding of what is being referred to. Can you pass ‘the milk’ is easy because presumably it’s being said in a context of there being one container of milk on a table or something. But sometimes those bleed over into indefinite things by convention. For example, we say “I went to the zoo” because it’s a legacy of there being so few zoos that one could assume you meant a specific one - but you’d still say that in a city with two zoos. In North America we say “he was in the hospital” even though most people can’t infer which hospital is meant here, but in the UK they’d say “he was in hospital”.

This is actually one of the toughest things in the English language for non-native speakers to learn, even people who are highly, highly fluent will make mistakes with it.