Traditionally we use 'pass the salt' to ask for salt at the dinner table when the food lacks salt. It's also a way to break the conversation up when someone has said something you do not want to answer or acknowledge.

Example:

- Men should be the slaves of women

- *eye roll* Pass the salt.

Pass the salt = give (me) the salt

Pass the biscuits = give (me) the biscuits

Pass (v) = give somebody something by putting it into their hand or in a place that they can reach it easily

By itself it sounds like an order or command so it should be said with please or thank you after it.