You can only send a direct message (DM) to someone who is following you.
DMs tab, tap .
Enter the name of a
Twitter users in the
As you enter characters, matching results appear on the screen. Tap the name when you see it.
Enter your message, and then tap
You can also send a direct message when you press and hold a tweet of the person you want to send the direct message to, and then tap
Send direct message on the options menu.