Once you and your friends sync a shared file library onto your computers, you may add, delete or edit files in the library together. Every change you make to the library would be automatically synced to others' computers.
Sometimes you and your friends may edit the same file at the same time. Your changes may conflict with each other's. In this case, Keeper would keep the first version synced to the cloud unchanged, while renaming the other version to a "conflict file". A conflict file's name ends with it's author's email address, plus the current time, e.g. test.txt (SFConflict email@example.com 2015-03-07-11-30-28).
In order to solve the conflict, you will have to manually sort out the differences together with your collaborator.
Source: Seafile Help