Genki Desu is one of those Japanese expressions that are used a lot and don’t really mean what you think they mean. You can use it as a greeting: O Genki Desu Ka? (お元気ですか - how are you), or to say you’re feeling fine (元気です - Genki Desu). The word Genki also means ‘energy’ or ‘vigor’. I am not an expert, in fact, there’s so much Japanese I can actually speak (shame on me), but Genki Desu is one of my favourites. Maybe just because it sounds so nice!