How do I fix Messages not working on iPhone?

At the very least do all 8 steps here, don't miss any out

1.    Settings, Apps, Messages,

2.    turn off iMessage   

3.    Settings, Apps, Facetime,

4.    Turn off Facetime,   

5.    Power down the phone

6.    Turn on the phone again 

7.    Settings, Apps, Messages, turn on iMessage, (wait a moment til it activates)

8.    Settings, Apps, Facetime, turn on Facetime

At the end ensure that your number and email appear in your send/receive addresses in those settings

You have asked us to guess everything about your situation. We don't know, for example:

• What iPhone model
• What iOS version
• What you tried
• What you saw
• What worked
• What failed
• What error messages appeared
• Whether the recipient uses an Apple device
• Whether iMessage has worked with this recipient previously
• etc.

What is it doing instead of working? What is it not doing? On what device and OS? You ate going to need to provide considerable more information for a yone to be able to help you.