Hi Arjey,
Welcome to the world of DAZ Studio. Here are some answers to your questions:
After you have everything you need in a scene click File - Save As - Scene...
Everything you have will be saved into the name you give for that scene. When you build a different scene you can load any other previously saved scene into the new scene. this way you can save individual characters, evnvironments and props as individual scene files. There is more to this of course. I save props as Export... Wavefront Object so that I can import them later with drag and drop into the DAZ interface.
Watch all the youtube.com videos on DAZ Studio. Download all the tutorials available here on sharecg.com.
Good luck and happy rendering!