Many people ask the question: "How can I add an attachment to an email message on my iPhone?" The short answer is you must start off the message with the attachment. You cannot simply write a message and then add an attachment like you would on a normal email client.
To do this, follow these instructions below:
Step 1) Open up the Photos app or whichever app you have an attachment to send in.
Step 2) Click the button in the bottom left that has an arrow inside a square.
Step 3) Click "Email Photo."
Step 4) Continue filling out the rest of the email message as you normally would!