do i need to save the photo, to another album or how do I manage them

I concern was that the My Photo Strean said it only held it there for 30 days. I suppose I don't understand what 30 limit means form what I must do.

1. Does this mean I have 30 days to get it? And once down loaded it is now permanent in the almum 'my photos stream'. If so how to know what has not be downloaded?
2. How do I remove from stream to the permant album. I tried dragging it to other. but it does not remove it. Now I have a housekeeping mess.
3. I don't want to sweep the dust under the carpet, and I am sure Apple or someone had a idea of optimal use????