The 14th mitzvah is that we are commanded in the actions1 involving tzitzis.

The source of this commandment is G‑d's statement (exalted be He), "And it shall be to you as tzitzis…And they shall attach a thread of blue on the fringe of each corner."2

Although we have a basic principle,3 "The lack of blue thread does not prevent one from fulfilling the mitzvah of white thread, and the lack of white thread does not prevent one from fulfilling the mitzvah of blue thread," [and, as explained in the 11th Principle,4 this would be sufficient indication that they are independent and count as two separate mitzvos,] nevertheless, they are not counted as two mitzvos.

This is stated explicitly in the Sifri:5 "One might think that there are two mitzvos: the mitzvah of blue thread and the mitzvah of white thread. However, the Torah says, 'And it shall be to you as tzitzis. 6' This shows that it is only one mitzvah, not two."7

Women are exempt from this mitzvah, as explained in the beginning of tractate Kiddushin.8

All the details of this mitzvah have been explained in tractate Menachos.9