A local branch is not synchronized to any remote repository by default - it is kept private to you until you explicitly publish (or "push") it.
Perform one of the following actions:
In the Sidebar drag the local branch onto the remote repository item that you want to push it to.
Right-click the branch in the Sidebar and select "Publish Branch..." from the contextual menu.
NOTE:When publishing a branch you can choose to "track" the newly created (presumably remote) branch.