Hi there, How does investing in POSB invest saver work?

It is a Regular Savings Plan (“RSP”) that allows you to invest via a GIRO arrangement on a monthly basis. You can choose either invest in the Nikko AM Singapore STI ETF, or the ABF Singapore Bond Fund, from a minimum of $100/mth. Units will be bought in on a regular basis for you. Do consider your risk appetite, your investment horizon, as well as the costs of investing.

More information is available here, and you should take some time read them before deciding if this is for you:

https://www.posb.com.sg/personal/investments/in...

I just started on this with Nikko sti etf .. meant to be for a Long term investment via dca..

as per any investment, there is no guarantee of returns but you have to weigh your risk appetite and ability to sustain this over a Long enough period to make the costs meaningful. Gains will not be immediate as we cannot time the market.
also how “good“ a return can be subjective according to various investment goals that you have. Eg some are happy with the 2% almost risk free interests from ssb, some don’t think it’s good enough if the returns cannot beat inflations. For me, anything Beats the paltry 0.05% interests given by standard bank savings account.

in fact, one of the reasons I try this is because I am trying to get an extra 0.3% interest in my Dbs multiplier account for fulfilling the investment category.