Here are some examples:
* Unhappy: Not happy
* Unbelievable: Not believable
* Unbreakable: Not breakable
* Unlock: To remove the lock, the opposite of locking
* Unwrap: To remove the wrapping, the opposite of wrapping
It's important to note that "un-" can sometimes have slightly different meanings depending on the word it's attached to. For example, "undo" means to reverse something, not necessarily the opposite of "do".