To create an alias for git checkout.

git config --global alias.co checkout

Instead of git checkout, you can now run

git co

Some common aliases to consider adding

git config --global alias.co checkout
git config --global alias.st "status --short"
git config --global alias.lg "log --oneline --graph"
git config --global alias.uncommit "reset --soft HEAD~1"

To see the list of aliases in your Git configuration

git config --list | grep alias

If you want to add this as an alias you will need to add ! to qualify it as a full Bash command

git config --global alias.alias "!git config --list | grep alias"

If you use dotfiles, you can add all your aliases directly to your .gitconfig file.

[alias]
	br = branch
	cm = commit -m
	co = checkout
	st = status