Following illustrations would help you in understanding of the above formula usage -
Example 1
You bought a fund at an NAV of Rs.25.32/-
The NAV appreciated to Rs.33.45/- in 8 months i.e., 240 days.
Then, the annualized return as calculated using MS-Excel is:

fx=POWER(number,power)-1
=POWER(33.45/25.32,365/240) - 1
=POWER(1.321,1.521)-1

which is 0.5272 or in other form, 52.72%