The Shulhan Aruch (Orah Haim 24) writes that it is a Misva to hold one’s Sisit with his left land near his heart while reciting the Shema each morning. According to the teachings of the Arizal (Rabbi Yishak Luria, Israel, 1534-1572), one should collect his Sisit already while reciting the paragraph of "Ahabat Olam" before Shema, when he reaches the words "Me’arba Kanfot Ha’aretz" ("from the four corners of the earth"), which alludes to the four corners of the Tallit.
According to Kabbala, one should hold the Sisit strings in between the pinky and ring finger on his left hand. Rabbi Haim Kanievsky (contemporary scholar in Israel) maintained that this applies equally to right-handed and left-handed people; even a left-handed person should hold the Sisit strings in his left hand.
Later in this Siman (chapter), the Shulhan Aruch records the custom to look at the Sisit strings and place them upon one’s eyes while reciting the words in the third paragraph of Shema, "U’r’item oto" ("you shall see them"), which speaks of the importance of seeing the Sisit. The Shulhan Aruch expresses his approval of this practice, noting that it serves to demonstrate "Hibub Misva" – one’s love and affection for the Misva of Sisit. According to the Arizal, one should look upon the Sisit strings throughout the recitation of the third paragraph of Shema. The Mishna Berura (commentary by Rabbi Yisrael Meir Kagan, 1839-1933) cites from earlier sources that whoever places the Sisit strings on his eyes while reciting the third paragraph of Shema is guaranteed not to lose his vision.
The Rama (Rabbi Moshe Isserles, Poland, 1525-1572), in his glosses to the Shulhan Aruch, records the custom to kiss the Sisit after looking at them. Different customs exist regarding when the Sisit should be kissed. Some kiss the Sisit each time they recite the word "Sisit" in Shema, while others kiss them also while reciting the phrase "U’r’item Oto…" and immediately after completing the Shema.
The Kabbalists teach that one should continue holding the Sisit even after completing Shema, until he recites the words, "Ve’nehemadim La’ad U’l’olmeh Olamim" in the paragraph following Shema. At that point, one should kiss the Sisit and put them down.
Furthermore, the Shulhan Aruch writes that one should look at the Sisit when he dons the Tallit, just before reciting the Beracha.
All these practices are well-established, time-honored customs that one should make a point of observing, and they should not be neglected. Seeing the Sisit strings helps remind a person of his obligation toward the 613 Biblical commands, and, as the Torah writes, prevents him from straying from Misva observance.
Summary: Upon reciting the words "Me’arba Kanfot Ha’aretz" before Shema, one should take hold of his Sisit strings with his left hand and hold them near his heart until he recites the words, "Ve’nehemadim La’ad U’l’olmeh Olamim" after Shema. It is proper to look at the Sisit while reciting the third paragraph of Shema, and many have the custom to kiss the Sisit each time they recite the word "Sisit." One should also look at the Sisit strings when he dons his Tallit, just before he recites the Beracha.
