From the Start screen, swipe left to display the Apps list.
Alternatively, tap All apps (located in the lower-right; may require scrolling).
Tap new (located at the bottom).
From the To field, enter a 10-digit mobile number.
Alternately, enter a contact name. As the name is entered, a matching contact may appear and can be selected at any time.
Alternately, tap the plus symbol (located in the upper-right), tap a contact then select the appropriate mobile number (if applicable).
Repeat this step as necessary to add additional recipients.
From the "type a message" field, enter a message.
Tap Attach (located on the left; above the keyboard).
Tap Photo or video.
Tap the appropriate folder (e.g., Camera Roll, Saved Pictures, etc.)
Tap the desired picture(s) then tap Done.
Tap Accept (located at the bottom).
Tap Send (located on the right; above the keyboard).