jj bookmark move main --to @-
git add .
jj git init --colocate
git init
The first command you mention is `jj bookmark move main --to @-`, which apart from the `@-` part, is easily read and does exactly what is written. It moves the main bookmark to the parent commit. The main difference to git here is that updating a branch is an explicit action. Jujutsu supports creating aliases and many users have a `jj tug` alias that moves the current closest branch to point to the parent commit. `git add .` just adds all changed files in the current directory to the current commit. That's an entirely different thing and Jujutsu takes care of doing that automatically.
The second command creates a git repository and while it is longer, I doubt the extra keystrokes will hurt you much. If it's too long, just alias it.
As for using `jj git`, since Jujutsu supports multiple backends, backend-specific commands require the `git` namespace. You generally only need it for cloning, pushing and fetching (with the option for aliases again). You'll rarely need to create a new repository or add a remote.