That's a very vague question with a number of solutions which may not work in every circumstance. There are a number of reasons for an NPC to be missing, and most of the solutions require research to find the NPC's code, and one or more console commands to fix them.
Perhaps a more specific question would get a more specific answer.
For instance, "Belethor is missing and his shop stays locked all the time." or "I'm at the quest marker for the Sybil of Dibella, but she's not here." Two common problems of somebody not being where they should, with completely different causes, and each solution being a rather lengthy post explaining how to fix it.
And even if you get somebody back to where YOU think they should be, THEY might think otherwise and simply walk off again. Or, in Belethor's case, you get him back and he still doesn't reopen his shop. This is because AI code or quest stages have been set that need further research and several additional console codes to fix, if it even can be fixed from within the game.
Of course, if you're playing on a console, let's just cut to the short answer: you don't.
The easiest answer, though, is "reload a save when they were where they should be, then don't do what you did to make them go away."
It should have come with the game, it may be on a sticker on the inside of the DVD case, or on the back of the manual.
Play It?
it means "with me" in the accusative (as in, sombody talking to sombody else) it means "with me" in the accusative (as in, sombody talking to sombody else)
It's basically about the high king's murder and dragons returning back to Skyrim.
Yes, you can.
no call sombody who knows what they are doing
I played both, and I would recommend Skyrim. There is simply much more you can do in it.
Skyrim. There's tons more gameplay and has the ability to generate an unlimited amount of quests.
as long as you have 2gb of ram, which is how much Bethesda have restricted Skyrim to use on any computer ( without the use of a mod), you should be able to run Skyrim, mediocrely
Any that suits your playstyle.
It should tell you if you need to update
No, After you leave it is impossible. unless you're on PC.