Help with camera roll etc

Hi

I have 8 gig of photos on my windows pc. I want to put these on my ipad. Below are a few questions.

if i take a photo using the camera - where is it stored? - roll or stream or both - whats the difference

again if I receieve a photo by email.

I only have 1 device, so is it worth having them in the stream - or is this for sharing? As you can tell I dont quite understansd whats happening here.

If in the stream? could I share a folder or picture with the girlfriends ipad?

next

If i put the pictures on a card and copy them to my ipad - again where will they go regards the above and getting backed up.

I read that they last 30 days? and up to 1000 photos - after 30 days do they dissapear or only from the stream? again help.

once uploaded, i take it they are on the hard drive (flash), so I could back them up using dropbox or skydrive - therefore they would be on my ipad and secure on the microsoft cloud?

any help appreciated

Thanks