Nested IF

[gebobs]

Lots of ways to skin that cat. Here's one.

On the left is the lookup table with the lower bound of your intervals under Score and the corresponding Level to their right.

To the right, enter a score into the cell in E2 and it returns the level in E3.

This is the formula:
=VLOOKUP(E2,$A$2:$B$6,2)

What that does is look up the value of E2 in $A$2:$B$6 that is either equal to or lower and closest to it. It then returns the corresponding value it finds in Column 2 of that range.