A pronoun is a word that stands in for a previously stated noun. While an antecedent is a noun, any appropriate pronoun represents. One simple source of the unclear antecedent is vagueness due to many possible antecedents. For instance in this example:
Jeff handed his father his glove.
a reader or a listener would be confused if ‘his' is referring to John or his father. Thus, it is unclear whether the glove belongs to John or his father. As a non-native English speaker, you have to be aware of the possibility of making statements with unclear pronouns since in some other languages there are different pronouns denoting differences in the noun or antecedent being used.