This graduate thesis gives a presentation of trigonometry in GeoGebra in the second and the third grade of secondary school. Since the trigonometric functions taught in the third grade represent a problem for most students, they are put in the focus of this thesis. In the first part of the thesis, the trigonometry is dealt with within the context of the existing and forthcoming curriculum in classes depending on the classroom timetable in some secondary schools. It also presents trigonometry through history, gives a brief insight into the teaching of trigonometry today and in the end it points out GeoGebra's characteristics, GeoGebraBook and GeoGebra Groups. In the second part the trigonometric ratios of the second grade are dealt with through GeoGebra. It also describes some of the most important GeoGebra tools such as sliders, checkboxes and texts which were most frequently used in the thesis. This is followed by a description of the GeoGebraBook Trigonometrijske funkcije in which most of the trigonometry of the third grade is processed. The thesis describes how some applets are used in GeoGebraBook, the purpose of GeoGebra in teaching and how it can be used by teachers and students, in and outside the school. At the end of the chapter, there is an example of a teaching lesson Sine and Cosine Graphs processed in GeoGebraBook created specifically for that lesson. The thesis is suitable for lecturers who want to approach teaching trigonometry in a different way. Various animations, videos, and quizzes can inspire students' interest in the subject, encourage students to study and research independently, create a positive attitude towards maths and show it doesn’t have to be difficult and it can even be extremely interesting.