Click on Start
Click on Computer
You should see used space and free space under the drive letter and beside the drive icon.
If it does not show the used and free space then right click on the drive
Click on Properties
To see how much is used up in "temp" folders and other such, right-click on the C: drive under Computer, click Properties and then in the box that appears click "Disk Cleanup." This will bring up a window showing how much is stored in various locations and how much disk space you can gain by deleting those temporary files.