Go to Settings > Messages to set options for Messages, including:
Turning iMessage on or off
Notifying others when you’ve read their messages
Specifying an Apple ID or email address to use with Messages
SMS and MMS options
Turning group messaging on or off
Showing the Subject field
Showing the character count
Blocking unwanted messages
Manage notifications for messages. See Do Not Disturb.
Set the alert sound for incoming text messages. See Sounds and silence.