Disney+ is a streaming service. When you subscribe to the service you can watch ad-free movies and tv-series that are available on the Disney Plus service.
Just like other steamingservices like Netflix you can watch from different devices: your (smart) TV, smartphone, laptop, tablet or console. There is also a possibility to download a serie or movie so you can have you kids watch it on the backseat of your car on holiday.
The list of movies and tv series is changing and can be different in specific countries but basically these studios are available on Disney+: Disney, Pixar, Star Wars, National Geographic (so it is not only fun, but also educational), Marvel, 20th Century Fox.
A subscription is about 7 dollars a month, and can be obtained on https://www.disneyplus.com/