The easiest way is to shoot the person in front of a green/blue screen, then you can do lots of things including making them appear and dissapear.

That may be Jsnkc but Jet's answer is by far the cheapest way to do it. no question, plus you don't have to try and do adjusting to pull out the blue/great/or whatever color screen you used in reflection light.

Well he never said the Cheapest way :)
If you're looking for cheap, then yeah, the other way would be cheaper.

The problem with the "other way" is that it assumes the background is essentially unchanged from one shot to the next. If you have anything else moving around then it too will disappear/reappear/jump when your subject disappears.

Yes and probably could make objects disappear one after the other with use of the shape tool.

I wonder if that is how they did it in "Bewitched", perhaps not , they never were seamless.

In "Bewitched" they used a far simpler technique. The director would tell everyone to freeze, they would add or remove the person/object/whatever, then resume action. In post they would slice out the footage while everyone was frozen and splice the film together to make it look like the change was instantaneous and magical. Look carefully and you'll see other things move slightly too. People's eyes may suddenly be looking a different direction, they may suddenly have exhaled instantaneously, a hand may be in a different position, etc.

I guess I felt that that was understood. perhaps I assume to much

Assume how do you say that again Ass-u-me right.

Yes - I was assuming a static background.

I believe the phrase is....Assuming makes an ass out of u and me ;)

I'm just glad to see that I'm not the only person here who knows that ;-)

I have used the method given by JetDV to make a person ( a ninja) slowly materialize into the view behind another person. It worked very well.