So ~/.tmux.conf overrides default key bindings for many action, to make them more reasonable, easy to recall and comforable to type.
Let's go through them.
If you are an iTerm2 user, third column describes the keybinding of similar "action" in iTerm2. It's possible to reuse very same keys you already get used to and tell iTerm2 to execute analogous tmux actions. See iTerm2 and tmux integration section below.