Its proportions are forgiving of minor errors. This is the foundation of how to write calligraphic letterforms.
There is no easy way to learn calligraphy.
So if you're serious about wanting to improve, it's always best to get a teacher sooner rather than later, so you won't have to 'unlearn' too much later.
And just because you are not holding your pen at a vertical angle for example does not mean that you cannot draw a vertical line! The thick-and-thin effect and small decorative tags or serifs which were created by our early nibs became the standard appearance for good writing.
Learn the ink, nib and paper combinations that play well together. In the Far East the problem was solved by making special brushes to paint the letters with. The learning how can involve a lot of mistakes, inky fingernails, wasted paper and frustration. The Carolingian Reform in the 8th century developed a roundhand to promote learning.
It could be compared with the English language: very easy to learn enough to communicate well, more difficult to use professionally.
The exact angle varies for different scripts - don't worry about this for the moment. It encourages good calligraphic habits. Our beginner course starts with an overview of the supplies that you will need to get started. The nib should not turn as you form lines and curves.