Conditional formatting based on adjacent cell?

[Custard Tart]

I have a spreadsheet which needs a basic RAG format based on the cell
adjacent.

For example column L contains the score, column M contains the empty
box to be filled with colour based on the RAG status.

It should be formatted as follows:
Less than 18 = Green
18 = Amber
27 = Red

I'm not sure how to link it to the adjacent cell?

Thanks!

 

[Don Guillett]

for col a, formula is
=b2=???

 

[David Biddulph]

In CF, use "Formula is", not "Cell value is".
If your active cell is M2, formula is could be =L2<18