If you're asking a waiter for coffee in a restaurant, either one means the same thing. Otherwise, 1. This is asking the other person to get the coffee for you. 2. This could mean the same as #1 OR it could be used to ask permission to get coffee for yourself. Hope this helps!

The difference between can and could comes in three flavors. This flavor is one of politeness. It is considered more polite to ask, "Could you open the window?"