The Proper Size of a Tallit Katan
By Rabbi Jaclyn Rubin
I am Observant and I Wear Tzitzit
The Shulchan Aruch covers the laws of tzitzit in Orach Chaim 8-12.
You can find these sources online in Hebrew and in English.
Hilchot tzitzit can be found in chapters 1-3 of Sefer Ahava of the Rambam's Mishnah Torah.
You can find these sources online in Hebrew and in English.
Arukh HaShulchan, simanim 8-24 can be found online in Hebrew, with English forthcoming.
Many (though by no means all) of the material on tzitzit comes from the Talmud in Menachot
See 38a-44a in Hebrew and in English