Ok, how best to explain this?
Each file is uploaded into your /tmp directory. So the ACTUAL files are stored there. What you have in PHP is the information about those files (inside $_FILES) which you can use.
Basically inside your loop you need to insert the information into the database and move the uploaded file from the tmp directory (specified by $_FILES["pictures"]["tmp_name"][$key]) to wherever you need it using the move_uploaded_file() function.