What are some simple video editor with Masking capability? I want to focus faces of an image and move that focus to each of the faces one by one with a delay.The other area of the image should be hidden/blurred 

(btw this is called masking right?).

Is there any simple opensource(or just free) software for doing this? 

A trial version would do because I need to make only one urgent video for now.

A good tutorial would be helpful as well.
An oldie question, but let's add an answer...

The answer depends on if the faces are moving through the frame.

If the faces are relative still, like a camera on a tripod and the persons sitting in front of the camera, any video editor with more than 1 video channel can do the trick. Just add a layer with something on it, a prepared semi-transparent PNG as a mask perhaps.

But more complex software is needed if the faces are moving or if you want a blur, instead of a semi-transparent mask.

If the faces are moving you need to track them, so the program needs to track it.

As @Shultc commented Both Blender and HitFilm can do this, and I would add Davinci Resolve.