Are you looking for a primer on Index Funds? Check out Index Funds For Beginners which gives an excellent introduction despite being discussed in a US-based context.

By periodically investing in an index fund, for example, the know-nothing investor can actually outperform most investment professionals. Paradoxically, when ‘dumb’ money acknowledges its limitations, it ceases to be dumb.
– Charlie Munger

The largest mutual fund in the world is now officially an index fund based on Wall Street Journal :

Pimco’s Total Return bond fund now manages $223 billion, compared with $299.4 billion for Vanguard’s Total Stock Market Index fund.

This means that Vanguard, with almost $3 trillion in assets under management, has 10% of its assets under a single fund – Total Stock Market Index Fund. In fact, Vanguard’s website lists the official net assets under this fund as USD$343.5 billion as of 31st July 2014 with an expense ratio of only 0.05%.

Vanguard Total Stock Market ETF (VTI)

Seeks to track the performance of the CRSP US Total Market Index. Large-, mid-, and small-cap equity diversified across growth and value styles. Employs a PASSIVELY managed, index-sampling strategy.