• Discarding local changes (permanently) to a file:

git checkout -- <file>

• Discard all local changes to all files permanently:

git reset --hard

• Switch to master and merge

git checkout master
git merge new-branch

• Local

git branch -d branch_name

• Remote

git push <remote_name> --delete <branch_name>

• Stash changes when you want to quickly switch branches

git stash

• Retrieve most recent stash

git stash pop

• List stashes and pick the specific one to pop

git stash list
git stash pop stash@{1}