How to search in the Study Catalogue:
Select your mode of study, programme and field of study and you will get to a page with a table including courses. The table is divided by semesters. For each semester it mostly lists compulsory, compulsory options and elective courses. If some courses (e.g. compulsory options) are not listed, they are not offered for your field of study in the given period, so you do not have to worry about them.
Read the instructions in the introductory section of the Catalogue as well as in individual courses!