There are 3 ways in which Singapore Airlines (SIA) recruit its cabin crew. The recruitment or interview may be either via online application (2 types) or Walk-in.
In most countries eg: Singapore, Malaysia etc the online interviews are by
1) submitting a video of the candidate (including personal particulars) or
2) simply submitting the personal particulars of the candidate (no video needed).
After reviewing the above online applications, the successful candidates will be asked via email to attend the face-to-face interview. Those shortlisted (the ones who were asked to submit videos) would skip the first round of the interview ("self-introduction"). The other shortlisted candidates will have to go through the "self-introduction" round during the face-to-face interview.
As for the Walk-in interview, candidates would have to visit the venue of the interview (see above last image) with the necessary documents and register with the receptionists. This category of candidates will go through all the rounds of interview starting with the "self-introduction" round.