It appears that your computer's hard drive has an area (called a 'partition') set aside for keeping recovery files in case something goes wrong with your computer. (It's also possible that drive E is actually an entirely separate drive but the use of a partition on your main drive is far more likely).
Either you've mistakenly been saving lots of big files (such as videos) onto that area [instead of onto the main part of your hard drive] or, far more likely, your computer has back-up software which has been creating regular back-up files and placing them in that partition without deleting earlier ones. Either way, that partition (or drive) is now running out of space.
Double-click on 'My Computer' or 'Computer' (depending upon which version of Windows you're using) and then double-click on Drive E. That will show you everything that's on there. (You might need to double-click on one or more folders to see what's inside them). I suspect that you'll find loads of back-up files, probably with dates in the file names. (e.g. backup01012, backup010212, etc). You can almost certainly safely delete all except the most recent ones but, if in any doubt, show the contents of that drive to someone who understands computers before actually doing so!