Ah, yes, the difference of は(wa) and が (ga) can be a bit tricky.
In the sentence: *コーヒーはすきですか？* -the particle は(wa) is used to mark コーヒー _("coffee")_- There is no real equivalent in English for the Topic particle は (wa). But to give you an approximate idea of the effect of は (wa) in English, we can use _"As for..."_ or _"Speaking of..."_. So, the sentence would roughly translate as _*"As for coffee, do you like it?"*_
Some notes on は(wa)...
*__は Wa Marks the Topic__*
A topic is the word about which the rest of the sentence provides information – in other words, anything that a speaker wants to talk about: an object, location, person, and so on.
:arrow: は (wa) marks a previously introduced and understood topic in the conversation.
:arrow: は (Wa) is used to mark something that is familiar to both the speaker and the listener, or something that is obvious and they are both aware of.
:arrow: は (wa) sharpens the contrast between two items, and can be used more than one time in a single sentence.
While は(wa) is used to mark something that is familiar to both the speaker and listener, が (ga) is used when a situation or happening is just noticed or newly introduced.