An index fund is a mutual fund or ETF that seeks to replicate the performance of an index, often by constructing its portfolio to mirror that of the index itself. Index investing is considered a passive strategy since it does not involve any stock picking or active management.
Studies show that over time, indexing strategies tend to perform better than stock picking strategies.
You can invest in indices with RM investment bank https://www.rmib.com/th/investments/assets/indices/ . There are very favorable conditions for this, such as tight spreads and a commission of $4 for a $1 million investment.
Because they are passive index funds also tend to have lower fees and tax exposure.