A common mistake beginners make is saying: 'I've invested in an ISA.'

An ISA is not an investment. An ISA (Individual Savings Account) is simply a tax-free bucket.

You still have to choose what kind of 'water' to pour into it.

If you open a 'Cash ISA', the water is cash (earning interest). If you open a 'Stocks & Shares ISA', the water is investments (like the Index Funds we just learned about).