When you're in the contact's record it is possible to send them a plain text email, this works in the normal way allowing you to add a subject line or even CC/BCC people into the email. What it also allows you to do is to send out attachments. 

These are files/items stored within your file management section of the system. To load file into the system, please click here 

Once the file is loaded into the system, you can simply click on the drop down which says "Attach a document" and this will open up a drop down list of any and all documents which you've loaded up and can now attach to the email you are about to send