I think you are still confused but it's pretty simple.
You only need to open 2 account.

Esaver or Dash

SSA.
If you look at the above, you will see 4 accounts under 2 heading,
A) Accounts
B) Investments
Under (B) Investments is the Securities Trading account which is just to tell you what's the total you have invested, it's not an actual account, more for reference only. You can ignore it. It's automatically created by default when you open a SCB online trading account.
Now for the meat.
Under (A) Accounts you have
1. Securities Settlement Account (SSA)
2. FCY Securities Settlement Account (FCY SSA)
3. Esaver/Dash
Esaver or Dash account acts as a saving/current account. It also acts as a bridge for you to transfer funds to 1 and 2. You cannot direct transfer funds to 1 and 2 from other banks. No way no how. You need either Esaver or Dash to transfer funds to 1 and 2.
What is SSA?
1 and 2 SSA are accounts in different currencies for you to buy/sell stocks.
This is your trading account.
As you can tell from the picture, 1 is in SGD, 2 is in USD. You can
open as many different currency account as you want and I encourage you to open all the available currencies,
it doesn't cost a thing. Just tell the person you want to trade all the markets and need all the FCY SSA open. The person will be lazy sometimes because it's a lot of paperwork.
So once you open a Esaver/Dash and a Trading Account(SSA), you can start to trade. All you need to do is transfer $$ into either Esaver or Dash and then transfer $$ from Esaver/Dash into the SSA. Use the SSA to buy/sell.
You need to
use the right currency to buy the stock.
In SGX, most stocks are denoted in SGD, some are in other currency like USD. Hong Kong Land Holdings is one, Dairy Farm is another.
You can also use the USD to buy US stocks!
I encourage you to open at least USD FCY SSA.
So that's about it, hope it's clearer with the picture.