Basically, RN its a webhook. Once active, you can view merge requests related to a task, when synced. Over time, we should be releasing a full fledged Gitlab bi-directional sync and app (similar to our Github app here: https://github.com/marketplace/tara-ai)
Our Github app also allows you to view stale PRs that are blocking the sprint. We should have similar functionality for Gitlab over the next few wks.