with the clouds, its harder than just adding effects.
you need to add a mask with the pen tool on a copy of a video you want it on.
then on the timeline click the drop-down and right click the mask. (if nothing shows up make sure you are in the right composition panel and that your mask is closed.)
once you right click the mask click track mask
a panel will show up on the right.
click the forward triangle
when your mask it tracked both ways, slap some clouds between the masked video and the original video.