Scenarios You'll Probably Hit
"My push failed, it says rejected"
Someone else pushed before you. Do a Pull first (it will merge/rebase your changes together), resolve any conflicts, then Push again.
"I want to throw away all my local changes and start over"
Right-click each file → Discard, or if there are many, right-click the branch/working copy → Discard All Changes.
danger
Cannot be undone.
"I committed to the wrong branch"
Reset (soft) the commit off the wrong branch, checkout the right branch, then cherry-pick or re-commit there.
"I want to grab just one specific commit from another branch"
Cherry-pick: right-click the commit on the other branch → Cherry Pick.
tip
In SourceTree, the graph view in the main window is the best "visual" aid — each circle = a commit, each line that branches off = a branch, where they join = a merge.