Fountain pens are similar to quill pens in that they both have a metal nib that lets ink flow down to the paper. But fountain pens are different because you don't have to dip the nib into ink after every one or two words. Fountain pens store ink inside them.
Here is an example of writing with a fountain pen. Notice that the harder the writer presses down, the wider the line. Also look how long the ink stays wet.
Next, here is a demonstration of filling and cleaning a modern fountain pen.