Fountain pens have been around since the 1800s and the aspect of a fountain pen that makes it write differently from other pens is its nib. If a fountain pen's nib is bent, then the ink will not flow properly, if at all, and you won't achieve the smooth writing for which fountain pens are famous. If your fountain pen nib is bent, you can attempt to repair it with the appropriate procedure.
Insert the razor blade in the pierce hole of the nib.
Apply pressure gently and cautiously to the nib in the direction you wish it to move.
Remove the razor blade and test the nib by writing with it on a piece of paper. The fountain pen's ink should flow and write smoothly. If the ink has lines in it, won't flow at all or flows too wet, then repeat the process until the nib is perfectly straight, which will cause the ink to flow correctly.
If all else fails, you can simply replace the bent nib with a new nib.
Older fountain pens' nibs are much more brittle than new ones, so you must be extremely cautious when attempting to repair an older fountain pen's nib to avoid breaking it.