Question

What is the

HEAD
master [branch]

?

What should I choose for the “Source ref” and “Destination ref”, respectively?

Answer 1

You see this screen in Egit Push URI documentation:

That is where you define the refspecs:

A “refspec” is used by fetch and push operations to describe the mapping between remote Ref and local Ref.
Semantically they define how local branches or tags are mapped to branches or tags in a remote repository.
In native git they are combined with a colon in the format <src>:<dst>, preceded by an optional plus sign, + to denote forced update.
In EGit they can be displayed and also edited in tabular form in the Push Ref Specification and the Fetch Ref Specification and other dialogs.

The “left-hand” side of a RefSpec is called source and the “right-hand” side is called destination.
Depending on whether the RefSpec is used for fetch or for push, the semantics of source and destination differ:
For a Push RefSpec, the source denotes a Ref in the source Repository and the destination denotes a Ref in the target Repository.

Push Refspecs

A typical example for a Push RefSpec could be

HEAD:refs/heads/master

This means that the currently checked out branch (as signified by the HEAD Reference, see Git References) will be pushed into the master branch of the remote repository.