Fountain Pen Basics
Here is some preliminary information to get you started if you've never seen or written with a fountain pen before.
Just what is a fountain pen?
Quite simply, it is a pen that contains three things: a nib (which does the writing), a feed (which regulates ink flow), and some supply of ink that is carried within the pen. Believe it or not, workable fountain pens aren't actually all that old; L.E. Waterman's pen was not invented until 1884.
For thousands of years, the challenge was to create a pen that had its own ink supply. People wrote by dipping a pen (which can be made from quills, bamboo, steel, gold, whatever) into ink, writing a line, dipping again, and so on. This gets tedious pretty quickly.
So how do I write with one?
Contrary to popular myth, normal fountain pens require no special training to use. You write with them as you would any other pen. It helps greatly if you write "properly" as taught in elementary school, so if your grip is weird it may impede your use.
Remember, shiny side up with the nib. This point should be obvious, but it never fails to amaze me how many people try to write with it upside-down or sideways when I let them borrow my pen.
It helps to use a shallower angle and a "correct" grip. Fountain pens write poorly when held vertically. The shallower angle is vastly better for you ergonomically.
Finally, don't press too hard when writing. Unlike ballpoints, which require firm pressure to write a clear line, fountain pens will write with zero pressure. The more flexible and expressive nibs can be permanently damaged by excessive pressure. Just remember that when writing with a fountain pen, write lightly.
So how exactly does it work?
Quite simply, it is a regulated leak; only surface tension and air pressure keeps the ink inside. The nib is derived from older dip-pen nibs, which are in turn derived from quills. This is what gets ink on the paper. There is also an ink supply that sits behind the nib; the challenge in creating the fountain pen was to make sure the ink comes out at exactly the same rate as it is used.
Capillary action gets ink on the nib onto the paper; this in turn pulls more ink from the ink reservoir. The bit that makes fountain pens work is the feed - the ink regulator. This little thing sits under the nib and lets air into the ink reservoir at the same rate that ink leaves the reservoir. Ink is kept in via air pressure. If the rate does not match, the pen skips or blots. Lewis Waterman's feed is usually credited as the first one that worked well.
This is quite different from a ballpoint or roller, which uses a small rolling ball to transfer ink from the cartridge to paper. It is very much like writing with a super smooth dip pen, but without the dipping.
Why doesn't anyone use them anymore?
Actually, people still use them, with good reasons. In some parts of the world (especially Europe), fountain pens are still used in schools. This is also true for especially stuffy schools (like some Catholic schools) in the US.
The thing that killed widespread use of fountain pens is, quite obviously, the cheap ballpoint. Economically, it is impossible to compete against Bic at ten cents a pen; a few dollars buys you all the pens you'll ever need, assuming you don't lose too many of them. Non-disposable pens are a small segment of the market; fancy pens a smaller segment of that, and fountain pens an even smaller segment of that. As a result, most young people in the US have never seen one or even know what one is.
Care and Feeding
Fountain pens are generally not disposable pens, so there is some small amount of maintenance involved in keeping them in perfect working order for years.
Use fountain pen ink
You should stick to ink that is explicitly marked for fountain pens. India ink and enamel paint are not suitable. Most waterproof inks contain shellac, which will horribly clog the feed.
It's probably a good idea to clean the pen every now and then. Yearly is probably adequate if you are using that pen regularly. You should also consider cleaning the pen whenever you change brands or colors of ink. This prevents old ink from diluting the color of new ink. Also, some inks are slightly acidic and some are basic, and it would be moderately hilarious to have percipitate form inside the pen as a result of ink mixing.
To clean the pen, rinse the nib and section in cold or lukewarm (not hot) water. Then fill a cup with water and repeatedly operate the filling mechanism until the water expelled runs clear.
You should also clean it if you are going to be storing it for a while. No sense in giving ink a chance to dry out and clog in the pen.
Do not use as projectile weapon
If the pen lands on the nib, chances are good that the nib will be bent. This is nearly impossible for a non professional to fix and generally renders the pen useless. Save your Bics for office warfare (they are probably free there anyway).