When collaborating in an asynchronous way, it may happen that 2 members edit the same section of content, leading to a conflict.
When trying to merge a draft, GitBook will automatically detect the changes that conflict with the changes of an other writer, you will be asked to resolve those conflicts.
You will be able to see the paragraphs that created conflicts, showing both content versions created. You can then pick the version you'd like to keep in order to resolve the conflicts. Once all conflicts have been resolved you will be able to save and merge your content.