May I know how do funds help you to invest across global markets and diversify? Or would it be enough to just invest in funds in Singapore?

Singapore is a rather small and limited market. The best returns come from relative returns, ie. one country, currency or company is better than another, by virtue of that, the wider your investment universe, the more investment choices there will be and the greater the ability to generate relative returns. Funds provide that access to a diversified portfolio of holdings across asset classes, or geography, and that typically would help achieve a consistent long-term return.