How do use a .bin file?

Depends. Those are generally used for data on cd's or dvds, I believe. I was going to type out a whole explanation but, as always, google makes me lazy.

What are .bin files for?

So, open up notepad or Microsoft word, or whatever you happen to have, type out

FILE "C:\locationoffile.bin" BINARY
TRACK 01 MODE1/2352
INDEX 01 00:00:00

Save the file as a .cue file. Then either mount it on a virtual drive such as Daemon Tools or burn it to a CD or DVD.

Play. Enjoy.

Scan the sucker with your antivirus and antispyware first before opening/executing it.

I use .bin files all the time. You can't execute them, at least not to my knowledge. My use is in embedded systems. Software is written in something like C++, when it's compiled various extensions are created such as .hex (for hexadecimal) .bin (for binary) and .bcd (binary coded decimal).

When burning a chip .bin or .hex are the most common. Sometimes if the embedded system has drivers for the computer and you would like the user to be able to update the chips firmware (like printers) .bin files will exist for recovery or update. In this case the .bin file does become an executable of a sort, but at least to go into the inner workings of chips would take some time (an update of the bios could be in .bin format as this is updating a chip on the mother board for example)

Although strictly speaking .bin files could be almost any kind of data that are stored in a binary format. They can then be accessed from another application, but not directly executed. Again explaning how to create an executable that accesses other files would take some time to explain as well.

I just had a look at individals response, in which case it would seem metadata on CD's and DVD's is also in binary format. Very useful and is what gracenote use for CD identification used by itunes and ipods and just about everyone, at least it is if we are talking about the same thing.