This is a second screen you carry with you. It's the size of a laptop screen but sharper — 4K in 15.6 inches means text is crisp and you can fit a lot of detail in a small space. Useful if you travel for work or want to extend your laptop at a coffee shop without lugging around a full desk monitor.
It powers and gets video from a single USB-C cable if your laptop supports it, which most recent ones do. There's also a mini-HDMI port if you need to plug in something older or a game console. The whole thing is thin enough to slide into a backpack sleeve.
The screen is bright enough for indoor use but not gaming-grade fast. Think of it as turning your laptop into a two-screen setup that packs flat.