uh... TS, you need to know the definition first:
Normal Postage will be sent to your letterbox, and lost mail will not be accounted for.
Registered Mail will be sent to your doorstep, and you need to sign on a document given by the postman. If no one's at home, then they will leave a notice for you to go retrieve it at the post office stated.
normally the fees for Registered Mail will be paid by the one posting the mail. He/she will then get a tracking number (or RA number) from the Post Office. you can get this number from the person posting the mail to you.
with the RA number, you can then visit this site (
http://www.singpost.com.sg/ra/ra_article_status.asp) to check on the status of your delivery, whether it's still in the Post Office or it's been sent out.
edit: and oh, Registered Mail is more expensive than Normal Postage. when you buy things online, always opt for Registered Mail. doesn't hurt to spend a little more to make sure your items reach you safely.