Pad Thai noodles is one of the most popular Thai dishes, perhaps second only to Tom Yum Goong, the Thai famous spicy seafood + mushroom soup.
Thin dried rice noodle, also called rice sticks are soaked in warm water until soften, stirr-fried, then shrimps, or chicken, or for vegetarians tofu is added, egg(s), ground peanuts, bean sprouts and /or other vegetables, chopped garlic, spices etc to own taste.
Don't soak until the noodle is soft enough to eat, or it will turn into mush in the wok. Just do it until it's pliable, then drain well.
The key to good Pad Thai sauce is tamarind pulp (for the sour flavor), Tamarind is a kind of tropical fruit that comes in pods.
Aside of the main ingredient, cane sugar, the other ingredients are: fish sauce (for the salty part), palm sugar (for a slight sweetness), and paprika or Thai chilli powder (for the spice).