I would like to get this effect were when the lower third is sliding in the screen I want to know how they keep the white lower third bar sliding in without the picture of the world showing till the end were the 7 News logo is. How can I accomplish this?, I have tried doing it but no luck as i make the white lower third and add the slide effect and put the world as a separate layer they basically slide together from the start till end, While i want the world being shown till the end just like in the clip were the 7 News logo is. I have also tried just adding the slide effect then as the white bar slides to the end i quickly add the world but its not very good and not what i want.
You need to use a track matte. Think of it this way:
The lower third doesn't actually move in, instead it is already there, but you have a separate rectangle shape that comes in and makes the lower third appear. You can just create a solid and animate it in from left to right. Place the solid above the lower third and choose "Alpha Matte" in the track matte dropdown.