If you are a student, you can book a video conference from your Dashboard. You can only book video conferences for topics you have completed. Completing a topic includes earning enough XP (usually 30) in the relative dialogue space.
Once you have completed a topic and earned the XP required to book a video conference, you will find a new card below the name of corresponding topic in your Dashboard, which will allow you to book a video conference.
When you click on "Book videoconference" you will be able to select a date and time for the session:
Click on "Learn more and book" to access the details of the video conference and proceed with your booking.
Please note that all times shown for video conferences are in the local time zone selected in your profile. You can learn more about changing the time zone set in your profile here.