The letter is drawn by starting at the top left, drawing the roof, which extends down into the right-hand "wall". Then the floor is drawn by starting at the left, making sure a little "ledge" extends out further on the right (so it is not confused with Kaph, etc.).
The first letter in the Torah is Beth, forming Bereshith: "In The Beginning". There are many commentaries for why a Beth begins this seminal Qabalistic text and not an Aleph. One explanation states that Aleph was not used because it begins the word Arar, meaning "curse", while Beth begins Berakah, meaning "blessing". Another has all the letters line up before God, asking to be honoured with beginning the Torah and Creation. God chooses Beth, but keeps Aleph as the first letter, representing his unity (Kether).
Interestingly enough, if we take these first two letters together, Aleph Beth, we have Ab, the Hebrew word for Father. Thus, even the alphabet begins with the Father (God). The little "ledge" at the back of the Beth is an opening unto the breath of Kether, showing that these two letters are interlinked, like Force and Form. Beth always points to that which precedes it, just as the House points to the One who built it (and Aleph=1).
A further interesting point about Bereshith is that when we take the Hebrew, BRAShITh, and remove the three letters Resh, Aleph, Shin (RASh), which forms Rosh, meaning "Head" (related to the letter Resh), we are left with Beth Yod Tav (BITh), the spelling of Beth and "House". Thus, the Head (God) dwells in the House.
However, Rashith (RAShITh - Resh Aleph Shin Yod Tau) means "[the] beginning" (Beth can represent the preposition "in"), and thus Beth, which means "House" (Bayith), existed before the Beginning. B'Rashith. Beth Rashith.
The House existed before the Beginning. This is the House of God. But it is also the House of Israel. And what existed before the Beginning? Nothing. Nothing existed before the Beginning. So the House of God, the House of Israel, is Nothing. It is Ain. It is above the manifestation of Kether, because it is Unmanifest.
The Bahir says: "To those who seek to see the face of the King, but they do not know where the King is. First they ask the whereabouts of the King's house, and then they ask where the King is." When you find the House of God (Beth), then you will find God (Aleph)