From a technical standpoint, almost nothing is shot in 4K resolution. All movies and TV shows are 1080p or lower currently, with probably a few expectations. Most game consoles are barely going at 1080p. I think some very powerful PCs can force 4K, but that's about it.
It's like 3D, it's useless. It may become the standard years from now, but 4K is only worth wile on huge TVs, hell 1080p is useless if the TV is small enough.
For a quick resolution lesson, the numbers represent the pixel height.
480p is 480 pixels tall, 1080p is 1080 pixels tall, 4K is around 4000 pixels tall. The higher the resolution, the smaller the pixels.
"p" or "i" represent interlaced of progressive.
If you can't tell DVD from Blu Ray, you do not need 4K.