If you are shortlisted for the interview, you will be notified online and you would have to confirmed your attendance online; just follow the instructions in the email.
From here on, I would relate my own experience on the interview process for the scholarship at NTU. The interview was conducted in a meeting room, so there was a huge meeting table between me and the 3 interviewers (Not much of a chance to present your portfolio to back up what you're talking about).
The questions were more or less the same, like "In your opinion, what do we look for in a scholar?
", "Do you have the qualities of the scholar that we are looking for and why?
For the NUS interview, there was only one interviewer, the Deputy Director.
The interview was held in a rather small room, so it helps if you bring a portfolio of your past achievements/projects or even photos.
And there's other options like the Tuition Fee Loan scheme and Work Study Scheme (work on campus and earn /hour; you can earn up to 0 per month).
I was also invited for the ASEAN scholarship by NUS recently. You will be required to fill in a CV form and email it back to the official.
The one seated in the middle, directly opposite me, is the dean of Admissions, Dr. The other 2 interviewers were professors (but I did not take note of their names or faculty, was too nervous haha).
What I did was, I was polite but most of the time, I was just being myself.