It uses a persistent changeid to model a change mutating over time, like Gerrit uses Change-Id in the description footer, and unlike git.
Jujutsu can be colocated with git and use .git as its backing store; every jj change revision is a git commit.
When you use jujutsu, you tend not to use branches any more, and think in terms of changes and chains of changes (i.e. stacked PRs, what Gerrit calls Relation Chains).
Jujutsu makes it very easy to work with a chain of changes (stacked PRs), letting you update commits in the middle and automatically rebasing the rest of the chain, without forcing you to interrupt work and resolve conflicts if there happen to be any (so, unlike git rebase -i with 'edit' on the commit you want to update).
IMO if you like the Gerrit workflow and the way it handles chained commits, if you switch to jj for two days of work, you'll never want to use git again.