One of the most important factors for improving the personalization aspects of learning systems is to enable adaptive properties to them. The aim of the adaptive personalized learning system is to offer the most appropriate learning path and learning materials to learners by taking into account their profiles. In this paper, a new approach to adaptive personalized e-learning systems is proposed. This approach provides navigation on course materials, as well as navigations on course topics and domain concepts. In this approach, in addition to the difficulty of learning materials and course topics, students' levels of knowledge and students' understanding degrees on the course topics have also been taken into account. The Item Response Theory and Law of Total Probability have been used for estimating understanding degrees. The performance evaluation of the proposed approach has been tested by using the exam and project results, as well as grade point averages of the students from the Computer and Instructional Technology Department. The test results show the accuracy of the proposed method. It is believed that this study can improve the effectiveness of the adaptive e-learning system.