How to start straight into cam mode?

I've played a few wads that when you begin the game, instead of starting off with gun in hand, you find yourself following the cam around a bit, then eventually it leads back to the character and you can begin playing the game.

Can someone explain to me how this is done?

well,those wads seem to have an open script like this:

script 1 open
{ ChangeCamera(1,1,0);
  // some movement stuff for camera 1 here
  ChangeCamera(0,0,0);
}

northsea.wad uses the camera effect you mentioned. You can figure out how it works by opening the wad in DoomBuilder and XWE

your script should look like

#include "zcommon.acs"

script 1 OPEN
{
ChangeCamera(#,1,1);
}

Note the "#" in the script refers to the tag number of the moving camera thing in your map.
farhaven uses "1" in his example. Northsea.wad uses "7"

In your map you should place a moving camera thing (9072) to define the starting point of your camera's journey.
You must also place Interpolation points (9070) to define the path of the camera.

Thank You all, I'll have a look into this today!


EDIT:

Ok, I got it down now, thank you again!