How do they do this in films?

[Spike]

For example, when two persons in a film are speaking to each other, you can see cuts between their faces.
Is it right, that the filmmakers for example shoot the whole scene with the camera on the one and then do the scene one more time with the camer on the other face. And in the post-production they cut it in the right way together - is that right?

[Raikus]

Usually that's the case. Sometimes though they'll use two cameras and film each angle at the same time.

[aclockworkjj]

Depending on how you are shooting it, both ways will work....at times though you need to be careful not to break 180 degrees as it will change the perspective of each subject...

[RegularKarate]

Crossing the line was considered hip in the early nineties... like on Homicide (the show, not the Mamet flick), that's one of the reasons I really didn't like that show.

[Cecil]

what line? 180 degrees??

[sphinx]

spike: it's called shooting coverage

imagine two people facing each other, standing 2 metres apart.  also imagine a line going straight through the center of their bodies off into infinity (so it looks like they're on a cabob).

when cutting the scene, if the angles are standard, you can't cross the cabob, or everything will appear reversed and your audience will explode

in conclusion don't combust your audience

[MacGuffin]

This may help:
http://www.mavart.com/art-film-line.html

[Cecil]

oh, yeah.... THAT line. well sure, if you dont want your audience to "combust"

[aclockworkjj]

I think I might have to break the 180 line now, cause I am dying to see an audience combust!  

Serious, yeah, that's exactly it...if you shoot from 2 different sides, anything noticeable in the background (a prop, point of reference) will flip sides as well....not a huge deal, but it's just a continuity thing...thats why, say 2 people talking...one is over one's right shoulder and the other shot is over the other person's left shoulder (assuming they are facing one another)...

[Sleuth]

I thought this was called a reversal