Can't see animation after exporting to video I started using Blender a few days ago...

For some reason, after I rendered the animation to a video file, I was left with this grid (see screenshot). How do I go back to the 3D Viewport where I can edit the animation? The wierd thing is that I can see the camera's perspective just fine in the upper right. (I'm using Blender 2.77a)
Hover your cursor over the grid and key Esc until the grid goes away (probably twice).

What has happened is that because you selected Image Editor in the Properties panel > Render tab > Render dropdown, your computer rendered your video by switching the screen that was previously there (a 3D Viewport) to a UV/Image Editor.

I generally select New Window, because then you can simply X out of the window once it is done.