Note: this module requires a branch and merge license
It is possible in Matrix to create a branch of an existing project and later to merge back the changes from the branch into the mainline.
This is mainly meant to support release or feature branches and hotfixes / updates of releases releases.
It is also possible to push changes from the mainline to the branches. This operation is called push to distinguish it from the merge. The push operation can be useful if you want to keep one common set of items (e.g. some shared user needs/requirements or risks which are used in multiple products).
Tips for branching and merging
Try to avoid it - branching and merging is always a challenge
If you branch, branch late and merge early - the bigger the time between branch and merge, the more changes, conflicts and questions you will have
See an explanatory VIDEO on the basics of the branching & merging principles: branch & merge example