"Turn" just means to pretend that you have finished a row even though there might be some stitches left on your left needle. It's used to perform shapings. I've seen this on socks and hoods, but I imagine they can be used for many more shapings. Hope that helps.
I would recommend investing in cables for a number of reasons:
1. They are more travel friendly.
2. I think they are easier to manage in terms of elbow room when knitting in public.
3. They are lighter.
4. You can do kewl things like magic loop.
5. They take up less space/easier to store.
Hope that helps too.