What does it mean to hold down the shutter on a diana f+ camera? how long do i hold it down for?

i read the manual that came with the camera... and I'm not sure but some of it says that for different effects I should leave the shutter open for hours and sometimes days? I dont know if that is true.... i think leaving the shutter open after you take the picture is supposed to make it look dreamy and stuff? But how long am i really supposed to leave it open and can i move the camera while the shutter is left open, or does the thing i'm taking picture of have to stay still?