What should I do next after setting up a CDP account? I am 20 this yr but not really sure how to start investing?

My advice is that its importance to increase your financial knowledge first and understanding your personal risk appetite! This would require some effort put into research and self-reflection. Take the time as you are still young and in no rush. 

Some questions: "Am I investing in hopes of realising it all in the future to fund my child's future education/buy a house?" or "Do I want it to be an alternative source of annual income that can come in terms of dividend?" 

I would recommend investing 50% in a market portfolio like S&P500 ETF as it historically yields 10% return and has a general upward trend. Another 50% can be other individual stocks that you like and see a potential of 10% return. Diversification is always important. There is no reward for bearing unnecessary risks. 

While building up your knowledge, you can think about investing in low-risk savings plans (e.g. from banks, SSB) first to gain some extra interest, instead of keeping cash in the bank.

Accumulate once every 3 months and put it into a S&P 500 ETF quarterly! The historical returns are 10% and I would say it is much better than saving bonds​​

I would recommend you looking into investing in ETFs as they are diversified already, which means they carry lower unsystematic risks.

In particular, I think the S&P500 is a good choice for two main reasons. Firstly, it has historical returns of 10% per annum over the last 80 years, proving its amazing track record. Secondly, the US market is so big that it basically represents the global market, and it is quite impossible for the global market to collapse completely.

Hope this helps