In order to join a society, you need to go on that society's page, and from there you can purchase the membership by adding it to your basket and proceeding with the payment for it.
In case of any specific questions - even questions about joining fees and memberships - the best thing to do is for the student to contact the society/club directly through the contact details and social media each group has listed on their page. This way the student would get the most accurate information from a member of the society.