You will need:
An Apple device
An email address from someone with an iMessage
Step 1: Go to Message App
Go to the bottom of your screen and choose the Message app. It may be In a different place than mine is because I have things switched around.
Step 2: Push the Button at the Top
Push the pen and notepad icon at the top right.
Step 3: Enter Email Address
Enter the email address in the top box. If you click on it and it is red, it is invalid. It will not let you send an iMessage to this email if that is the case. If it is valid, you can send a message.
Step 4: Enter Your Message
Enter your message in the bottom box. When you have finished typing, press the 'send' button.
Step 5: Done!
Your message has sent!