Interview at South Africa high commission for critical skill visa application

Hi All, I had applied for critical skills visa , i don't hold an offer form a SA company currently. i had made my application with SAQA membership certificate and critical skill certificate from professional body along with all required documents on 11 oct 2017. I have received an email from VSF, stating that i have to appear in south African high commission for an interview on 30th nov. I tried searching, however could not get any details on someone's experience who has attended such an interview. Can someone here help me with details of what will be this interview all about, is there anything i should be prepared with? If someone appeared for such an interview can they share their experience? Regards, Jeet