Crew Chief can display subtitle overlay of what the chief, spotter and you say. This only works with the game running in windowed (or borderless windowed) mode.
To enable this use the setting "Enable Subtitle overlay" in the
Properties. Once enabled you should see a subtitle bar at
the top of your primary screen.
By default the subtitle window will be shown with settings to
adjust it, before the window will accept input you have to click
the checkbox "Enable input" on its titlebar, once enabled you can
move the overlay window to your desired location and change its
settings which are pretty much self-explanatory.
Dont forget to save settings once done.
To show/hide the settings/titlebar press CTRL + SHIFT.
For Oculus users the overlay can be rendered as a separate
application window, allowing it to be added to the VR world -
enable the 'Enable overlay app window (Oculus mode)' checkbox in
the Properties screen.