When a developer pushes a new branch to a repository a branch plan is automatically created.

By creating a branch in Stash and/or through the Terminal, the branch becomes available in Bamboo under the "Plan Configuration >> Branches" tab after a periodically polling.

git checkout -b <branchName>

echo "hello world" > greeting.txt
git add greeting.txt
git commit -m "add greeting"
git push origin <branchName>

Unfortunately, a new Plan is not created automatically as stated under the Bamboo 5.6 release notes documentation.

Application link between Bamboo 5.6.0 and Stash 3.1.3 using OAuth only.

In Bamboo, "Plan Configuration >> Triggers >> Trigger Type" is setup as "Stash repository triggers the build when changes are committed".