To be like “a fish out of water” is to feel awkward because you are in a situation that you have not experienced before or because you are very different from the people around you.
e.g. “I don’t usually go to parties, I feel like a fish out of water in that sort of enviroment”
e.g. “The new girl is like a fish out of water, she doesn’t even speak English”
e.g. “My new job is completely different from what I’m used to, I feel like a fish out of water“