The Prefix Key

Every tmux command from the keyboard starts with the prefix: Ctrl-b. Press and release it, then press the command key. Ctrl-b c means "hold Ctrl, tap b, release both, tap c."

Why a prefix at all?

Your terminal already uses most keys — Ctrl-c interrupts, Ctrl-d logs out, Ctrl-z suspends. tmux needs a namespace that doesn't collide with anything, so it claims one two-key sequence (Ctrl-b + something) and leaves everything else alone. Inside tmux, Ctrl-c still interrupts your program; tmux only acts when it sees its prefix first.

The keys worth memorizing

You don't need all 90+ bindings. This set covers daily life (verified with tmux list-keys -T prefix on tmux 3.4):

Sessions

Keys	Does
Ctrl-b d	detach (session keeps running)
Ctrl-b s	list sessions, pick one to switch to

Windows and panes — see Windows and Panes for the full tables. The short list: c new window, n/p next/previous, " and % split, arrows move, z zoom, x kill pane.

Everything else

Keys	Does
Ctrl-b ?	list all key bindings (searchable help)
Ctrl-b :	command prompt — type any tmux command by name
Ctrl-b [	copy mode: scroll back, search, copy text

Ctrl-b ? is the escape hatch: if you forget a key, it's in there.

Changing the prefix

Ctrl-b is awkward — b is typed with the left hand while Ctrl is also left. Many people switch to Ctrl-a (like screen used):

# ~/.tmux.conf
unbind C-b
set -g prefix C-a
bind C-a send-prefix

The third line matters: it lets you send a literal Ctrl-a to the program inside (press Ctrl-a twice) — otherwise you'd have no way to type Ctrl-a (start-of-line) in your shell.

Check: after reloading (see Configuring tmux):

tmux show-options -g prefix

prefix C-a

Stick with the default for a week before changing it. Every tutorial on the internet assumes Ctrl-b; learn the standard first, then customize from a position of knowledge.