Un- (not)
Un-
Not (with adjectives); or reverse an action (with verbs).
Meera felt uneasy before her first stage show.
Unhappy
Not happy; sad.
Rohan was unhappy when rain stopped the cricket match.
Unlock
To open something that was locked.
Diya unlocked the gate with the big brass key.
Remember: Add un- to the whole word, with no letter dropped: un + necessary = unnecessary (double n), un + natural = unnatural.