I try to consolidate the above + add some, while I don't understand the original dialogues completely:
@Jack I hope / believe that you know that なにこれ is [not literally, but considering the negative tone] close to WTF, i.e. you should for sure not use that to express that you did not understand what the person talking to you meant!
サーブ means "serve" in the meanings of [at least]
Serving [in the sense of bringing to you + handing over food / drinks. NOT like "We only serve vegetarian food"
In ice hockey ;-) / soccer [I chose "soccer" instead of "football" partly to avoid confusion [as some people may incorrectly think that "football" means "American football" ;-) ]
It is not used in the more abstract cases of "to serve" e.g. when saying something like "serving a country", or, in @JACK 's example "serving in the Olympics as an athlete"
サブ means "sub" of the sense "hierarcically below something else" [So, "subway" or "submarine" does not use it; submarine (vehicle) is 潜水艦] [At least if it is a military submarine; I think that the 艦 MAY not be appropriate for a non-military submarine, but I also don't think you say 潜水船 either].