This skill is about saying something like "I have nothing to fear" or "There is nothing to think about". Russian has special impersonal constructions to do just that; they make use of negative predicate pronouns.
They are all formed by adding a stressed «не» to a corresponding question word, which should be either "who"/"what" or an adverbial question word (e.g., "where").
Use Dative to specify a person for whom this applies:
Note how the prepositions split pronouns formed from «кто» and «что». Only a few "simple" prepositions can do this, however:
It is also useful to stress that such pronouns are only formed from oblique forms of «кто» and «что», since they never act as a sentence subject. Words «не́кто» and «не́что» are not in this list; they actually behave as analogues of "кто-то" and "что-то" in their base forms, just of a higher style.
P.S. «как» does not produce such a pronoun. Neither do «почему́» and «како́й»