To learn more about what's happening on the International Space Station at any given time, check out NASA's frequently-updated ISS blog or their page about the research and development work happening on ISS.
Depends on your body type and metabolism and your routine. But usually it takes around 3 to 4 weeks for visible results. For me it took me a couple of months to actually see any progress visually.
When starting out on a strength training program, you can literally start to see results in 1-2 weeks; adding cardiovascular exercise can help you feel a difference (increased energy and stamina) in as little as 2-3 weeks, or weekly on some measured outing such as a hike.