This guide is addressed to those mathematicians who want to get acquainted with the basics of structure theory, although they have not yet (or already!) chosen this branch of algebra as their specialty. Therefore, in the selection of results, preference was given to those that either contribute to the development of theoretical-structural thinking, or are used in other areas of mathematics. For a more complete acquaintance with the theory of structures, you should refer to the monographs of Birkhoff and Sikorsky .. The latest achievements of the theory of structures are covered and the relevant articles of the collection "Results of science" . The necessary bibliographic instructions are available at the end of the book. There are also textbooks on the theory of structures known to the author .. Some of them are accompanied by extensive lists of journal literature. The present guidance is limited to specifying the authors of some of the results included therein.