Also, I think parts of the code should be explained a bit more and extended.
What is $_FILES ? Can you choose a different filename? If it has the same filename, will it overwrite without asking any questions? And what about the max file size? is the value in bits or bytes, kilobytes, etc. ? and must it be 2048000, or can it be larger or smaller? And where is the max file size called in the uploading script? is it even used?
No offence with that little rant, just constructive critique to enhance the tutorial further I think it's really good but could use a bit of explaining!