The international large capacity ballpoint refill has a more controlled feel compared to a rollerball. The ink is a paste vs a liquid ink which has a longer life span. The stroke of a ballpoint pen is in most cases indelible i.e. it cannot be erased.
At the tip of the ball rolls a ball socket supplied with ink paste. As the ball provides closure of the ink at the tip, no cap or other device is required to prevent the ink from drying out. Ballpoint pens are ready to write immediately after placing the tip on the paper as opposed to a gel pen, which may not start to write immediately. They may need to be "brought back to life" by a few vigorous strokes at times.
All Graf von Faber-Castell Ballpoint Pens are refillable. The pens come with a black, broad refill when the pen is purchased. If you prefer blue ink and/or a different size line width, you can find other options here.
If you have a pen where you need to remove the cap away from the barrel in order to write, that is not a ballpoint. Ballpoint pens have a propelling twist mechanism on the back end of the pen to advance the refill. Ballpoint refills are not interchangeable with rollerball refills. They are not the same size. The pens cannot be converted as well.