While in-game, you can use Quick Chat to communicate with players using preset messages. These messages can be customized in the Chat tab of the Settings menu.
While in a Party, you can use Party Chat to text chat to your friends on all platforms.
During a match:
Only Quick Chat can be seen by players on all platforms
Only players on your platform can see typed messages
For more info on voice chat, check out: How do I use Voice Chat in Rocket League?
If you are a child and your parent hasn't helped you set up your account, you may have a Cabined Account with different features. If you think you might have a Cabined Account, visit: Why does my Rocket League account say that some features are disabled?
Once parental controls are set up for your account, you may be granted access to additional in-game features allowed by your parent or guardian.