Conditional Formatting - Use a formular to determine which cells to format

I am new to writing custom rules for cell formatting, so I hope I explain my self clearly. I am looking to set up a rule where based on what is in the H Column ("OS" or "OD") the appropriate cells get highlighted with a green background color. in the F column E.g OS is stated for item 1 in the H column, so the OS cells need to be highlighted with a fill color of green for item 1 (F4 and F6), for item two F7 and F9 needs to have a green background color, item 3 (F11,F13,F15,F17,F19F21), item 4 (F24,F26,F28,F30,F32,F34) etc. I want to set up a rule so this can be automatically done. Thanks and I look forward to hearing from you.