The term "style" is used to describe the shape of the nib, the most common being regular, italic and oblique. 

Italic nibs are shaped rather like a chisel - broad and flat.  Not surprisingly they produce italic writing. 

They come in different widths and as an approximation, the broader line of the italic nib is about the same as the next size up in a regular nib.  In other words, a medium italic writes about the same width as a regular broad. 

Italic nibs are more difficult to write with until you get used to them and for this reason they may not make a good choice for an everyday pen.

Oblique nibs have their tip cut at an angle instead of square.  This means that the pen must be turned slightly to ensure that the nib contacts the paper properly.  This suits some handwriting better and also most oblique nibs produce a script similar to an italic nib.

Oblique nibs come with the oblique angle to the left or to the right.  The RIGHT oblique is more suited to left-handed writers.