Quiet Confidence is a gear perk that cuts your movement noise for a short time after a takedown kill. It helps you chain silent takedowns through an outpost without nearby guards hearing you move.
After you kill someone with a takedown, you make less noise while moving for a while. Use that window to reach the next guard or slip behind cover.
Wear Walker's Wolf Boots in the feet slot. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Stealth perks such as Stalker and Takedown Tagger fit the same play style, and so does Vaas' Wrath if you play Vaas: Insanity.