What are the different types of pens?

Fountain pens: 

A fountain pen have a special split nib available in different sizes which makes the lines thinner or thicker as you write, depending on what size nib you use. There are also nibs that can change the width of the line depending on how much pressure you put on it when writing, these are called flex nibs.

With a fountain pen, you can choose any ink you want to use and change the ink color as often as you like. The ink often comes in a bottle and is available in lots of colors and with different properties. Read more about ink for fountain pens here.

When you refill your fountain pen with bottled ink, you use a converter, which is a kind of container that is inserted into the pen. You dip the nib of the fountain pen into the ink bottle and twist the top of the converter to suck up the ink into the pen. Sometimes the pen can have other built-in functions, such as using a vacuum function to refill the pen with ink.

There are also ink cartridges that you can easily insert into your pen. It can be handy if you want to easily change the color without having to clean out your pen every time, or if you are traveling and it feels tricky to bring an entire ink bottle. 

Gel pens: 

A gel pen is a pen with gel ink. Gel pens have a water-based ink that is smooth flowing and highly pigmented. Often has a slightly longer drying time, so it might smudge if you touch it too quickly or use a marker on top of it. Fun to write with and offers intense and saturated colors!

Rollerball: 

Rollerball pens often have water-based ink that flows easily and provides a light and very pleasant writing experience. The ink flows more easily than with a ballpoint pen and even a gel pen. Because the ink is more watery, it may be good to use higher quality paper to avoid the ink bleeding through the paper. Similar to the ink used for fountain pens.

Ballpoint pens: 

A classic ballpoint pen has an oil-based ink that is more viscous. A little more pressure may be needed when writing with ballpoint pens than with, for example, a rollerball pen or gel pen. Is often fast-drying and waterproof.