The letter yod represents the creation and the metaphysical.
Yod is thought to have originated with a pictograph of a hand that ultimately derives from proto-semitic yad, hand, and it is related to the egyptian hieroglyphic of an arm.
Yod as a prefix designates the third person singular (or plural, with a vav as a suffix) in the future tense.
Yod as a suffix indicates first person singular possessive; av (father) becomes avi (my father).
"Yod" in the Hebrew language signifies iodine.
Two yods in a row designate the name of God Adonai and in pointed texts are written with the vowels of Adonai; this is done as well with the Tetragrammaton.
As yod is the smallest letter, much kabbalistic and mystical significance is attached to.
Yod, slightly larger than a dot, cannot be divided into components. It refers to the Name, that is One and indivisible.
Yod represents the metaphysical, the essence of things which lays in the small, free of burden such as space, time or matter. This implies that greatness can be achieved through humility. (source: Maharal)
Yod also represents the idea of unity within multiplicity, of one whole that is comprised of parts. Yod as we see is a single point, but its value is 10. It shows us that many grains of sand are used to make one pot, many pages make up one book, many drops of water make up the ocean. There are many occurrences in the world, but they all stem from one God, perfect and indivisible.
In Kabbalah, yod represents the 10 sephirot,attributes/emanations.
Below you can see the movie of the production process of a clay prototype of a hebrew letter.