GoKawiiljj is the name of the CLI for Jujutsu. Jujutsu is a DVCS, or "distributed version control system." You may be familiar with other DVCSes, such as git , and this tutorial assumes you're coming to jj from git .
So why should you care about jj ? Well, it has a property that's pretty rare in the world of programming: it is both simpler and easier than git , but at the same time, it is more powerful. This is a pretty huge claim! We're often taught, correctly, that there exist tradeoffs when we make choices. And "powerful but complex" is a very common tradeoff. That power has been worth it, and so people flocked to git over its predecessors.
What jj manages to do is create a DVCS that takes the best of git , the best of Mercurial ( hg ), and synthesize that into something new, yet strangely familiar. In doing so, it's managed to have a smaller number of essential tools, but also make them more powerful, because they work together in a cleaner way. Furthermore, more advanced jj usage can give you additional powerful tools in your VCS sandbox that are very difficult with git .
I know that sounds like a huge claim, but I believe that the rest of this tutorial will show you why.