The Samsung NX series are good cameras, so if your start learning how to use it in manual mode you'll see an improvement in your pictures.
But it's not just about going from auto mode to manual, it's also about learning how to compose a good shot, and how to get the camera to capture it best.
I would say while you are learning, stick to Auto Focus (AF), but learn how to get the camera to focus on the thing you want. If you went to manual focus and didn't get it completely in focus it would ruin a good shot no matter how great your exposure settings were.
Learn about aperture (f-stop), shutter speed, ISO and how they all relate. Then once you're well practiced at getting the exposure right, then work on focusing yourself.
There's nothing wrong with using Auto Focus, and you can get the camera to focus where you want by using the Focus Points. The NX5 has 15 focus points (in a grid across the image), so you just pick the focus point you want to use for that shot and let the camera focus on that point.
Practice taking photos outside in good light, then you don't have to think about flash. Built in flash on any camera is bad. That Samsung can go as low as ISO 3200, so it should be sensitive enough to take photos indoors without flash, but you'll have to take it off the auto-ISO setting.
Follow some youtube tutorials or read the manual on how to change the exposure settings in manual mode or you could also try the Aperture Priority mode (A on the top dial) or Shutter Priority (P on the top dial). These will give you the option to set either the aperture (f-stop) or shutter speed and let the camera work out the rest of the settings.
Give it a go, experiment.
