Another good link for some basics:
http://electronics.howstuffworks.com/fiber-optic.htm
Can they be used for anything?
Any kind of data transmisison, yes. This includes actual data from computers (internet) or data from voice (PSTN). However, because fiber optics is able to transmit huge amounts of bandwidth, it is generally used for backbone or mainline purposes(for both internet and phone).
Another thing that has been overlooked is fiber optics transmission of cable TV signals. For cable systems, fiber is used as mainlines to connect the headend (main central station of a cable system) to hubsites for different serving areas. The information transported between hubsites and the headend include not only internet traffic, but TV programming as well.
As mentioned before, fiber optics is used to carry phone traffic as well. Analog phone lines are switched at a local station and, depending on the destination of the call, will end up being multiplexed onto fiber optics as well as potentially 100/1000s of other phone conversations.
If your using them does your ISP/Phone company have to be some kind of specific fiber optic company
Your ISP/Phone company doesn't have to own the fiber optics. It is likely that at some point they lease fiber optics from another company.
I mean can I just switch my ethernet cable with fiber optic cables some how or would I have to get a different ISP?
What you seem to be confusing here is that your ISP probably doesn't server your internet to you on ethernet. DSL uses phone lines, and cable internet uses the same cable that cable tv uses. If you wanted to get fiber optics directly into your house, you probably wouldn't be able to.
If there faster, cheaper to maintain, and all around better why isnt everyone using them?
It has to do with the implemention costs. It would be EXTREMELY pricey to bury and run fiber to every home. Not to mention, no ISP would have enough backbone infrastructure to support having that many people having that much bandwidth at once. At this point, cable internet providers currently aren't even close to the amount of bandwidth that they can potentially use with regular coaxial cable. My cable internet ISP now is supplying me with a 7Mbps down/1Mbps up connection. Using the same modem that I have now, if they had enough bandwidth to supply, I could get a 38Mbps down/24Mbps up connection.
