When you are a beginner in calligraphy, you should find sometimes tricky to draw the serif of some letters. A serif is the small decorative end of a letter, it makes a style beautiful and unique.
According to my observation, there are several ways to draw successfully a serif. The chronology, the direction and the number of strokes depend on each individual skill. It's like drawing a circle, some people will do it clockwise, and other prefer the counter clockwise manner.
Finally, calligraphy is an art, then any artist has thousands of reasons to draw a serif in his/her own way.
Here are some examples of letter with serifs: