I'd like to know who's talking about what within my country at this minute, real time - to get an idea of what topics, so I can join in. How can I do that?
The easiest way to go about it is to use Twitter Advanced Search. There you can search for twitter conversations while limiting the search to tweets from users near a certain country or a city.
Another advantage for mastering Twitter's query language is the ability to filter the search results not only by location but also by virality, for example: "show all tweets from the UK which have more than 100 retweets or 200 likes"