Short answers, pulled from the story.
Ralph McQuarrie painted a golden humanoid figure in 1976 that drew directly from the female robot in Fritz Lang's 1927 film Metropolis. George Lucas selected Anthony Daniels for the physical performance after hearing about this reaction.
Filming Star Wars proved challenging for Anthony Daniels due to the restrictive nature of his costume which barely moved, cracked easily, and had no ventilation system inside. The costume took two hours to put on each day and removing the headpiece required thirty minutes of careful work.
C-3PO first appears aboard a Rebel ship that is boarded by Imperial forces in 1977 before Princess Leia hides him and R2-D2 in an escape pod jettisoned over Tatooine. Jawas capture them there and sell both units to Owen Lars.
C-3PO appears in The Force Awakens with a red left arm and fluency in seven million forms of communication. He reunites with R2-D2 who reactivates after being shut off for years during their adventures.
Captain Raymus Antilles takes ownership of both droids and orders C-3PO's memory erased because this decision protects the Skywalker children from their father and the newly created Galactic Empire. This occurs when they pilot the ship to Polis Massa where Padmé gives birth to Luke and Leia.