Enter copy mode
copy mode
// what it does
Prefix (Ctrl+b) followed by [ runs the `copy-mode` command, dropping the active pane into copy mode at the current cursor position. From there the pane becomes a read-only scrollback viewer where navigation and search keys work instead of being sent to the shell. This is the primary way to review output that has scrolled past the visible screen.
// shortcut
Ctrl + b[
// gotcha
Ctrl+b is only the default prefix; if you've remapped it (commonly to Ctrl+a) the binding changes accordingly. Once inside, your normal shell keystrokes are intercepted by the copy-mode key table until you quit with q.