To attach a file, simply click on the paperclip icon, select your file and hit the green send arrow in the bottom right corner to send the message.
Note: you will need to enter a message to accompany the attachment before it will send. Supported image formats are: png and jpeg (or images taken directly from your camera). Supported document formats are: pdf, doc, docx, odt, xls, xlsx, ods. Maximum file size is 2MB