Just bring along your identification documents to any bank and
request to open an account lo. Do take note that an initial deposit
of $100/500/1000 (more details available on banks' websites) may be
required to open one, and from what I was told, you can't open more
than one account with a bank, so if your current account is with
DBS/POSBank, open a new UOB one.
Since you're 17, and it seems that you're planning to shop
online, I would recommend applying for a debit card at the same
time as well. For that, once again, you can read up more about
applying for one on the website of the respective bank you're
opening an account with.