Private UCAS applicant

a buzzword is for if you're applying through your school/college, so as a private candidate just leave it blank

Can someone please tell me if I’m applying as a private candidate, which option do I have to choose? As in there’s an option to put the “buzzword”

Who is providing your reference?
If you're getting a reference from a school or college that is set up as a UCAS "centre" then they may want you to add a buzzword for them to add your reference. This is not related to where you're sitting your exams.

My private tutor is going to be my referee as my former school refused to do the reference and predict grades. Even the exam centre I’m sitting at disagreed be my referee. So in that case I have to apply as a private candidate and put my private tutor’s email to write reference?

Yes if your reference is coming from a private tutor then you need to apply as an individual and not through a centre using a buzzword

Who is providing your reference?
If you're getting a reference from a school or college that is set up as a UCAS "centre" then they may want you to add a buzzword for them to add your reference. This is not related to where you're sitting your exams.