Drawing a card is a form of "adding a card from the Deck". If "Blackwing - Breeze the Zephyr" was drawn by a card effect, then you can Special Summon it. Because of this, the card "Thunder King Rai-Oh" had to clearly make an exception in its lore, and the card "Drastic Drop Off" had to clarify that drawing is considered adding a card to the hand.
Every turn during your Draw Phase, you normally draw one card from your Deck. (In the OCG, from March 21, 2014 onward, during the first turn of the duel the player who goes first does not conduct their normal draw that turn.)
Incidentally, there is a difference between “number of draws” and “number of cards drawn”. The number of draws refers to the number of times any number of cards are drawn, like when resolving "Hand Destruction", as both players draw 2 cards at once. However, cards like "Heart of the Underdog" only facilitate drawing one card per effect activation, but the effect can activate any number of times.
If a player is unable to draw a card because they have no cards left in their Deck, that player loses the Duel.