We don't really use pitons very much anymore. Some climbers will use them on mixed mountain routes and other will use them for high end aid climbing, but even in these venues pins are certainly less used than in the past.
There are two reasons. First, modern clean climbing equipment like nuts and cams have replaced the widespread need for pins. And second, modern pitons tend to damage the rock. Every pin placement subtly changes things until you have very well-defined pin scars.
The Canadian guide Mike Barter has put together a very nice video on pitons and piton placement. Check it out below:
There are two notes that I'd like to make about Mike's cleaning method.
First, some climbers will use a "cleaner carabiner" that they clip to the pin while pounding on it. This is then attached to the climber. This is so that the pin is not dropped while taking it out. The cleaner carabiner is commonly a very old and very beat-up carabiner. It's important that it is not a carabiner that you will be climbing on, as it will likely be struck by the hammer when the pin is being cleaned.
And second, Mike clips two quick draws together to pull the pin out. While this is fine for an occasional pin, climbers on big walls that require a lot of hammering will use a funkness device to pull out pitons. This is essentially a metal cable that has been designed specifically for this purpose. To see a funkness device, please click here.
Practicing with pitons is a tricky thing. The fact that they damage the rock makes them heavily frowned upon. I would strongly suggest that ground-school with this kind of hardware should take place primarily in areas where there is little to no climbing, otherwise someone may get very upset at you...
--Jason D. Martin