On the Raspberry Pi, this is a huge leap from the Raspian included Scratch - it might be daunting without any realtime graphical preview to the first time user of euch an environment. It is however, a progressional step for young (&old) learners to the world of scripting and programming concepts.
Creating games, apps etc happens using the IDE type editor built in to AGK. You can test builds on the host machine, or by using the broadcast feature which will send the compiled build to your Android or iOS device.
The language used is specific to AGK but is based on, I believe, a modern version/variation of BASIC. It's much different from my ZX Spectrum days, but is easy enough to follow if you have used other scripting languages.
Having just spent a short while with the Pi version, I was certainly impressed with the whole experience. The performance was much greater than I expected - tested on a Pi 3. I compiled some of the included projects and they all ran fine. I didnt need to adjust graphics memory or anything like that.
One of the strongest features of this release for the Pi, is the inclusion of all the demo / tutorial files from the main desktop version. This is a superb offering for those interested in programming or game / app development. All of the files can be loaded in and inspected to see how things are constructed. It's definitely something to consider if you own a Raspberry Pi and interested in learning how games can be put together.