In the words of Paarthurnax: "It is an... artifact from outside time. It does not exist, but it has always existed. Rah wahlaan. They are... hmm... fragments of creation." They are pieces of creatia, and possibly intrinsic to Aka's being.
It should also be noted that the prophetic ability of the Scrolls is only a small fraction of their power..
Sorry, it was a very specific use. The curse was specifically that no one would remember the name of any mortal who wore the cowl. The Elder Scrolls can show any piece of information. Because the Scroll was more powerful than Nocturnal, the names are remembered as long as the cowl is not actually being worn. You can't change history with them, just view it without the bias of the historian, as we saw in Skyrim.
These, and there's the out of game explaination, in that the elder scrolls is the physical game you're playing.
Each scroll tells of an event (each game) that can occur, depending on the perspective the viewer look at it (the player). Usually, it tell of a hero (the PC) who will do stuff (how you play).
And just like how everyone plays the game different, so do the elder scrolls read from a different event.