This is the 369th most frequent Hungarian word.
használt
Used.
Here, 'használt' functions as an adjective describing the noun 'autó' which means 'car', indicating that the car is pre-owned or second-hand.
Ez a használt autó nagyon jó állapotban van.
This used car is in very good condition.
In this case, 'használtam' is the past tense, first-person singular form of the verb 'használ', which means 'to use', indicating an action done by the speaker.
Nem használtam még ezt a számítógépes programot.
I have not used this computer program yet.
Here, 'használt' again functions as an adjective, modifying 'ruhák', meaning 'clothes', to describe them as pre-owned.