Sword Name: Needle
Owner: Arya Stark
Material: Castle-forge Steel
Forged at Winterfell as a gift for Ayra Stark. She was just 11 years old when her half-brother Jon Snow gave it to her right before leaving for the Wall and Night’s Watch duty.
Jon wanted something to fit Arya’s stature and designed a thin, light sword. Arya had never wanted to be a “lady” and was even the one to name her sword.
“Sansa can keep her sewing needles, I’ve got a needle of my own.” 
It is at King’s Landing where Arya learns to “water dance”, a series of quick steps and jabbing with the sword, much like fencing. Her teacher, Syrio Forel, is a master swordsman from the isles of Braavos.
Arya’s first kill come when she and Sansa are leaving King’s Landing in haste after her father’s arrest. After stumbling across the ransacked carriage, Arya starts to dig in her trunk for Needle when a stable boy grabs her and in the struggle the blade accidentally runs him through. Startled, Arya runs.
Finding herself watching her father’s beheading, Arya starts to draw Needle from its sleath but she is headed off by a knight’s watch recruiter, Yoren. Yoren then pretends she is a boy named “Arry” to keep her safe and get her out of the city. They keep this charade up while on the way back north to Winterfell. Here she meets Gentry, who is a blacksmith apprentice that asks her is she stole Needle noticing its is castle forged steel. Gentry is curious when “Arry” said it was a gift.
Yoren and his men are attacked by Lannister’s men at the Riverlands. Captives are escorted to Harrenhall after Yoren is killed. Polliver takes Needle from Arya and kills Lommy Greenhands by stabbing the boy through the neck.
Arya, while with the Hound, runs into Polliver and hatches a plan to get Needle back. He Hound doesn’t agree but when Arya makes her move he has no choice but to help her out. He fights Polliver. Arya, having recovered Needle, kills Polliver and leaves with the Hound.
Her next kill, number 3 with Needle if you are keeping track, is Rorge whom the Hound and Arya meet on the road. Rorge threatened Arya back when they were with Yoren and after the Hound gets his name Arya stabs him in the chest.
After that Arya hides Needle in rocks when trying to start a new life so that no one could recognize her. She leaves Needle and will not come back for it for some time.
*This is a show summary only.