.bin files are large files that contain all files present on a CD. It can be used to create an image of your CD to harddisk. Afterwards, you can create a new cd from the bin-file. The cd will be an "exact" copy of the original.
The program that you use to make a cd from a bin needs the .cue file. This file tells the program what kind of data is in the bin. (like: "do I have to write the .bin as an AudioCD or a CDROM?")
There are also programs that can "emulate" a cdrom drive, starting from a .bin file. So when you load the bin in that program, it will show an extra drive in windows, acting like a normal cdrom that contains the CD (while the .bin is on your harddrive!)