The main skills correspond to the major sections of TOEFL iBT are: reading, listening, speaking and writing. These are also the main language skills important for effective communication, especially in an academic setting.
The TOEFL iBT unique feature is that the primary skills are assessed through independent questions and integrated to simulate the way English is used in real life.
The following table describes where to find these questions on the exam.
Primary Skills for the TOEFL
Skills Independent Questions Integrated Questions
Reading Yes No
Listening Yes No
Speaking Yes Yes
Writing Yes Yes