Top, far left: This is the Nintendo Switch itself, in home console form. The tablet-like portable bit is dropped into the "Nintendo Switch Dock" like bread into a toaster. The dock connects to your TV, so you can play the same games on-the-go and at home. Nintendo says the Switch is a home console, "first and foremost."
Top, middle: As you see in the image here, a woman is playing an unannounced Super Mario game. She's holding a traditional gamepad, and playing the game on her television. With Nintendo Switch, the Japanese game company is making a push toward more traditional video game consoles.
Top, far right: That said, you can take Nintendo Switch with you anywhere. The portable game console you see in this image is just the tablet-like bit seen in the first image, but removed from the Nintendo Switch Dock. It's also got controllers snapped onto each side, making it into a portable handheld game console.
Bottom, far left: No game discs here! The Nintendo Switch uses cartridges, similar to those used with Nintendo's 3DS handheld. It's likely that Nintendo Switch also has an online service for buying and downloading games digitally, but Nintendo hasn't announced as much yet. It's also not clear how much internal storage is in the Nintendo Switch handheld (or if there is any in the Nintendo Switch Dock).
Bottom: middle: Nintendo envisions a future where you'll bring your Nintendo Switch with you, set it down on a table, and play multiplayer with friends. Given that the screen looks to be in the seven inch range, and that the controllers are incredibly small, we're betting this won't be a much-used feature. Still! It's pretty neat that you could set it up somewhere and challenge a friend to, say, a match in the latest Mario Kart.
Bottom, far right: These are the aforementioned small controllers. These snap onto the sides of the Switch screen, turning it into a portable console. They can also be used individually, or snapped onto a controller at home for a more traditional experience. Nintendo's calling them "Joy-Con" — like joystick and controller, all at once.