/title
Only players near you can hear you.
You can type /whisper so people have to be really close to you
and you can type /shout for your chat radius to be increased.
Let's say you're taking cover behind a wall and there is an enemy sniper trying to kill you.
So you're like: /shout Enemy sniper, red building by point B!
And a squad comes to support you.
/radio is optional but not 100% needed.