This dissertation states that it is possible to construct minimal deterministic finite-state automata fast and using little memory. Two new construction algorithms are presented. An implementation is discussed. Compared to a similar algorithm by Dominique Revuz, those presented here use far less memory. The thesis states that it is possible to construct automata that guess canonical forms and categories of unknown words much faster than it is done by other algorithms. A new algorithm is given and discussed. An overview of the use of finite-state automata in natural language processing (NLP) is given. A new type of automata is introduced. A method for spelling correction is enhanced so that it can handle Polish words.