Folders are identified by the yellow folder while other storage drives (magnetic disks) are identified by little grey computer boxes. The bottom icon in this case identifies the CD drive (notice the CD).

As you can see above, the storage drives are labelled with letters of the alphabet.

The A: drive is always the stiffy disk drive. If there is a second stiffy disk drive it will be called the B: drive (the computer in the diagram to the left does not have one).

The C: drive is always the hard drive. This is a magnetic covered metal disk inside the computer box. You can see a picture of it to the left (in this case the cover has been removed so that you can see the disk)

The D: drive is normally the CD drive, but if there are other hard drives, the CD drive could be the E: drive (as seen in the pop-up screen above). The important thing to is to look at the little icons to the left of  the drive name. That will help you identify what type of drive it is.

Each computer's storage space is like a filing cabinet such as the one to the left. This storage space can be divided into drives (drawers). Normally a computer only has one hard drive (C:), but there could be several drives available to you if the computer is connected to other computers (and their hard drives) on a network (computers connected by cable).

Each drive (drawer) has many folders and each folder may have many files / documents. Folders are always identified on a computer by the folder icon.   

Files are identified by a variety of symbols.
In the pop-up screen above you can see that Word files are represented by the Word icon.